For those of you that like to over analyze ever single thing you do on the golf course and keep track of it Golfity.com is for you. Golfity stores, tracks and analyzes all of the data you write down on your scorecard: number of putts, fairways hit, greens hit... Click here to check out a sample of their stats page.
My favorite thing about Golfity.com is the golf course analysis. The way it works is you can input any course into their system, then anytime you play that course you enter your scores and the play by play of your round. Golfity then analyzes that course and how you play it. This to me can be helpful particularly if you tend to play a few holes poorly. You can plan some course management to improve your score.
I personally don't need more distractions on the golf course like writing everything down as I'm playing. I do track my putts, but I don't do anything with that info after the round other than add them up. I think Golfity.com is a useful site for many, but I don't think I'll ever use it.