1-2 pages is generally recommended for a resume. What about for LinkedIn? If it should be longer, what parts of a profile should be covered in more detail?
LinkedIn and resumes are very different things.
A resume is (or should be) a carefully targeted document customized to appeal to a specific job opening or organization. Of course it needs to get to the point and be concise. What you exclude in a resume is as important as what you include.
LinkedIn is far more fluid and versatile, people are surfing "you" based on connections or search terms. You have no idea who will look at it nor what they're looking for. The description you put for each past position should take that into account but that doesn't really imply anything about length. LinkedIn is mostly about your connections. As such, it is probably good to include all past positions on your profile.
The same way you can have a short and a long version of your resume, or a resume and a full CV, you can use different online profiles to give a short overview or a full-view window to your professional life.
I tend to think it's best to give a full-detailed version, and that if they're not interested in looking in there for what they need, then it's their issue. Plus it makes you more marketable as you register on more people's radars, by way of having more surface for matching keywords.
Unfortunately LinkedIn doesn't provide the option to have a short view and long view, so if you really need this, I'd say host a short version on your personal site or Google+ page, or on StackOverflow Careers, and the long version on LinkedIn. Or the other way around. If you have a personal page, it's actually probably best to have it become the "focus point", and to have all other online profiles be short versions pointing to it. Makes it easier to maintain and avoids too much duplication.
You want an the experience section of your profile long enough for former coworkers to find you. Just listing companies and no details can make it hard for them to know if they have the right Casebash.
A few sentences will help the recruiters to find you with the search tools. If they see that you might be a potential employee they will contact you for the resume. The request for your full resume doesn't take very much effort on their part.
They are looking for you to respond, in fact they need you to respond. So they ask for the resume. Their search tells them what specialties you have, what city you live in, and if your experience has possibilities. But until you respond they have no idea how actively you are searching.
I am not sure they they will follow links in your profile. They want the search engine to find you, and having some detail in your profile helps them find you.
I also agree there is no way to equate pages of resume to size of LinkedIn profile.
First things first - when looking for recommendations, pick your authorities.
It makes little sense to ask LinkedIn advice from some stranger in the street: they may have an opinion but it's hardly a trustworthy source of information.
Look for the sources you can rely on. One that naturally comes to mind is, well, LinkedIn themselves. Note your interest here is to certain extent mutual: they generally want your profile to be successful since this leads to their service being more popular, more in demand.
LinkedIn recommendations on profiles are provided in their learning center:
Other blog tag worth looking at is LinkedIn Tips. There, look for so called Guest Authors - these will be your "secondary authorities" so to speak. Their presence in the blog indicates that LinkedIn considers them important and you can use them as another source of information.
Another "natural source" of authoritative information is Stack Exchange.
I write natural since you decided to post here - this assumes you put certain authority into what you find here. Thing worth taking into account is that Stack Overflow has Careers service, with user profiles having much in common with LinkedIn.
Primary source of information on Careers are Meta Stack Overflow questions tagged 'careers'.
As of now, there are more than 1000 questions in this tag, including more than 300 related to profile (search results for 'profile' in the tag).
Those willing to apply information about Careers profiles at LinkedIn, need to account for certain differences in the structure and terminology. Probably the most straightforward way to "synchronize" your understanding is to import your LinkedIn profile into Careers to find which parts of profiles correspond.
Don't also forget remaining "natural" authority - doing your own research.
Simplest form of doing it is studying profiles of your connections. Learning how your colleagues write their profiles can be quite helpful. While studying profiles, try to find what reads good and what feels better to avoid.
The last but not the least, search the web. Top results for search phrases like LinkedIn profile howto, LinkedIn profile improvement etc often lead to bits of a good information.
Here are few examples to get you started:
Finally (the least authoritative part of my answer), here are some of my own findings based on studying sources like mentioned above.
"Summary" part of my profile is targeted at those making a quick decision whether to proceed with more detailed background check or not - recruiters, hiring managers, potential interviewers. I consider this purpose almost the same as the one of brief resume (except that my brief resume also includes short overview of my experience and my contacts).
In my experience LinkedIn character limit (2000) makes a good fit to 1-page of text. My initial version summary was about of that size (you may see above it's as recommended) but after investing some effort in making it read better I managed to condense it to about 1200 characters.
I found an interesting explanation for delicate differences that may be there between summary sections in LinkedIn profile and resume. I feel like in my case I better don't bother with that but it is worth taking into account anyway:
As for "Experience" section, it is targeted at readers willing to thoroughly check my background to take a serious decision like whether to interview or hire me. I imagine a reader saying like
If some... I don't know, obscure skill or, say low importance project can make a tie-breaking decision in this thorough check, I would not want to miss / forget it. That's why I try to accurately capture details of every position in every slot of "Experience" section, even explanations for the job changes. I try to make it easy to read, understand and verify.
That makes "Experience" part of my profile quite lengthy, but as far as I can tell it is rather expected. As I already mentioned, this section is targeted at those making thorough background check - while "quick readers" focus on another section (Summary).
A "side effect" is - as opposed to Summary, I can not simply copy Experience section from LinkedIn straight into resume, even into the long one. This is nicely covered in an article written by Gerrit Hall:
There's one difference between resumes and LinkedIn profiles... With LinkedIn, you are waiting to be found. With resumes, you usually are the one sending it out.
What's this change?
What doesn't change?