You can now link your PSN account that you made on your PS3, or using the PlayStation store for PC, with your account on the Official Playstation site.  Just log in on http://us.playstation.com and it'll prompt you to link your two accounts together.  This allows you to see what your friends are doing online, the game they're playing, or their last login time.  Unfortunately, you can't send text messages to them like you can on XBOX.com but it's still worth your time to link accounts.

The link doesn't work :s.

Can you view and compare trophies through the Playstation site?

@ Konnichiwa

Oops, I should have stated that it's only for the U.S. apparently. I thought that they were supposed to do this in EU too, a while ago.

Damned I really want to see my messages on PSN =/...

Mine works fine, I guess.

Not sure what is the point other than more e-penis waving...

Yeah, I'm not sure either... I believe it's a step in the right direction though.  I expect they will add trophies to this, and being able to message your friends online too, just laying the ground-work for it, probably.

Just linked mine. I'd been waiting for this ever since the PAL guys got to do this months ago.

Cool, they are just building now.