If one attended meetings for a professional organization (example: IEEE or Java Users Group) on a repeated basis, but did not actually join the organization with a membership, is it a good idea to list such on one's resume and LinkedIn profile? LinkedIn has a place on the profile specifically for organizations, but would it be misleading to list there?
If you can clarify the scope of your involvement as @Roger points out - then sure, do so. You can say something like "regularly attends meetings" or something similar. It's a nice point of reference, and I happen to know that at least one recruiter I know of pays a great deal of attention to some of these meetings, so it helps to trigger a memory of "hey I know that guy!" - hopefully it's a favorable one.
At the same time, beware of overloading your resume/profile. Make sure the key information pops out. I just read through 2 resumes of 3+ pages each, with tiny font and lots of words. It left me numb. I had no idea of who the candidates were or what work they were really attuned to. My strong suspicion was that they didn't know either and were just hoping someone could figure it out for them.
Keep in mind that your interviewer may not be that smart, and hone your resume to the focus of the kind of job you are applying for or looking for. If you regularly attend meetings but have no other skills and no plans to work in that part of this industry - skip it and highlight details that make you look like a good pick for the next job you want.