Is beer dangerous to drink past its "sell by" date? I have a bud light in a friend's refrigerator that has a date of May 14 2007. I have heard of people drinking beer after the posted date, but does it turn harmful after all these years if I drink it?
The pH of beer is low enough that no known pathogens can survive in it. That's why you never hear about botulism problems with home-brewed beer like you do with home-canned foods, for example.

Beer slowly changes over time. High gravity beers, like barley wines or imperial stouts benefit from this, and acquire richer flavors as they slowly oxydize. Belgian styles, like lambics do as well and the wild yeasts and bacteria continue to grow. However, even those have a limit -- eventually they will begin to taste very stale. 

Low gravity beers begin to taste stale much more quickly. If you are keeping them refrigerated, they may last for 6 months or more. Seven years is definitely way too long.

So it won't make you sick or harm you if you want to taste it. But it is extremely unlikely that you will enjoy it.