When asking whether you should worry you need to consider the following:
How often do employers google prospective employees and how thoroughly?
This happens more and more now as people put so much information online but perhaps not as often as people think. The intentions can be a mix of looking for examples of a persons work (particularly in the software industry) and looking for any warning signs not to employ that person.
The skill and thoroughness of this depends on the employer. Some will not be as tech savvy as others, there are still many older people in work who do not have a good grasp of computing or do not know about the information it is possible to find online.
What is the nature of the information?
If it is indicative of criminal activity, things like racism or particularly bad behavior like binge drinking and getting into a fight you should defninitely worry a lot.
If displays aspects of your character or past behavior that isn't illegal or offensive then you have to ask if it would cause an employer to have second thoughts about hiring you.
Unless it's particularly bad then this will not necessarily cause them to outright reject you.
If it's just personal information that you find embarassing then you do not need to worry as any decent employer should not be affected by it.
I would say you are probably the third option with a bit of the second based on the information you gave.
Where is it ranked on google under different combinations of search terms?
If it's not on the first page then I consider it highly unlikely that you need to worry. In fact if it's not in the top 5 then for the majority of cases you are probably fine.
Is it obvious before you click on it that it's about you sepcifically?
If not then this reduces the risk of clicking and even if you do click it would have to be practically beyond doubt you being referred to.
How possible is it to get the information deleted or hidden?
If it is an individual rather than a news site it will obviously be a lot easier. In your case it should be quite easy to do this as it is a friend.
Any things on social networking sites can generally be reported or have privacy settings changed. If your friend refuses to change the details you can potentially report the content depending on where the blog is hosted.
You can use search engine optimisation (or SEO) to outrank the bad results on google but it will take time.
You can also take a legal route but again this could take time and possibly money.
Can I take steps to address this during the interview process?
Probably only if the information is expressly mentioned. You can try to do some damage control anyway; if you think the information makes you look lazy, for example, you can bring up some examples of things you did that prove you aren't.
I've generalised this answer a bit to make it more useful for others. You may find this article interesting.