Athlinks.com might seem like like a Myspace/Facebook rip-off at first glance (you have a profile page, friends, etc). But the most unique and best aspect of the site is that by simply typing in your name it will crawl through the vast reaches of the internet to find the times of all the races you ran! (Well, as many as were timed electronically by a D-Chip or something similar and then posted online.)
So now you have a history of your races (you can always add any races it didn’t find as well). Athlinks also matches you up against your “rivals” based on your results. Now you can keep track of how well you are doing against your closest competitors.
One complaint: Athlinks brings in rivals from all age groups and I (and a lot of runners I know) only care about those in their particular age bracket (25-29 for instance).