Finding school friends on MySpace or Facebook is not a bad thing, and it's not unhealthy. It is simply reconnecting with your past, which is good for some people and bad for others. But even if you are contacted on either of these sites by someone you went to school with who you don't want to reconnect with, you don't have to. Someone finding you on MySpace or Facebook doesn't automatically mean you have to get back in touch with that person.
At times it could be a positive thing if someone you had a problem with in school contacts you through one of the social networking sites. They may very likely finally be apologizing to you for the way they treated you when you were in school together. If it has been long enough since you went to school with them, the person has most likely grown and matured and is not the same person who caused problems for you in school.
Being contacted by friends you went to school with can actually be a compliment. It means that person may be interested in getting back in touch with you and picking up where the friendship left off. And even if that's not the case, many people have an interest in seeing the directions their classmates lives took after you all left school. It's similar to a virtual reunion when a physical reunion may not be possible. In addition, you may have more in common with your schoolmates now than you did during your years of school. People you weren't friends with before or simply didn't know that well, can go one to become a part of your adult life.
Many people gain perspective on life the first few years after they complete their formal schooling. This new perspective can allow them to connect with former classmates in a way they never could before.
Finding old friends on MySpace and Facebook can be exciting. Seeing pictures of people you attended school with, and possibly grew up with can be a fun blast from the past. Many people will post old pictures from their school days, or pictures from events such as a wedding or a child's first birthday party. This can be a great way to remember the good times and to congratulate former classmates on their accomplishments, whether that be a whole family, or just a loving spouse.
In most cases it is perfectly healthy to find old school friends on sites such as MySpace and Facebook. Just because people grow apart doesn't mean that friendships can't be rekindled.