Well on the nice side, you can check up when your forum friends are online and how they are doing - give em a rail etc.
On the evil side, you might play against someone you considered weak, someone who you think you might usually beat.
If you can add them to your buddy list then you'll know when they are online. Not that I've ever done such a cold and calculating thing
Actually I've only ever added a few friends to my buddies and only on one site,
but I have written down names and notes of cash game players who tend to give their money away.
It's not evil, it's poker, they know theyre trying to take your money and you know youre trying to take there's. I'd much rather win money from someone I don't know...infact I'd much rather lose money to someone I don't know.
edit..lol Crapshoot