I have an early 2008 MBP, and Lion has been working fine for me, but it doesn't seem any faster (or slower) than Snow Leopard, nor does it take up more or less of a memory footprint than Snow Leopard.
So it is safe to say that you will see similar performance with Lion than you did with Snow Leopard.
Is it worth the upgrade? The major feature for laptop users is the trackpad gestures, but since we are using old MBP models that still have the button and smaller trackpads, many of these gestures aren't really possible. I mean, they work, but they are harder to do with the smaller trackpad.
The other features are nothing really game-changing in my opinion. I really really REALLY like Mission Control, but if you go around and read some of the threads, some people hate Mission Control. The features of Launchpad can be obtained in Snow Leopard by easily making your Application folder a stack on your dock. Auto save and Versions is nice, but since I've used computers for so long (and have lost many files along the way) I have basically become addicted to saving, so those features don't really help me. The new Mail seems good at first, but after using it for most of the month, I can honestly say it is just a Apple's version of Gmail.
So it is up to you. I think it is worth it just because of Mission Control, and because it is only $30. But, people will disagree with me.
