I used it many years ago and located my best friend from the neighborhood where I grew up. Unfortunately, we lost contact and both moved away from the area.
I thought back then that the site was confusing. I wasn't really sure how to navigate around it.
Honestly, I am on Facebook, and have connected with many many more people from the old neighborhood and classmates from school then through classmates.com. Now that I think about it, I don't even think anyone has ever attempted to contact me through classmates.com, LOL.
Even our high school class has its own Facebook page, and we have connected through that, as well as our reunions and various peoples achievements announced through the Facebook page.
All this to say, I'd suggest you create a Facebook account before creating a classmates.com account.