Will upgrading to Lion boost performance and responsiveness? I remember going from Leopard to Snow Leopard was a huge performance boost.

Going to Lion, is it going to be the case? Read so many reviews yet none of them discussed this (many discussed gestures and mission control, etc).

I'm running Core 2 Duo 2.0 Ghz with 4GB RAM and Nvidia GeForce 9400. Late 2008 Macbook unibody.

EDIT (for future me doing google search): It works very well. Performance is quite the same as Snow Leopard. Should wait a bit for spotlight indexing, and don't plug in time machine drive while spotlight index!
All of the press / industry coverage is focusing on the huge usability changes (and that mirrors the marketing that Apple is doing).

Some notable exceptions are the new Safari which runs some benchmarks like web app and JavaScript significantly faster.

The major changes under the hood speak more to security, sandboxing and plumbing the new multi-touch interface, encryption, auto save, auto revisions rather than speed.

It is too soon to tell if speed is much better, but once people adapt to the changes, the idea is we will be much more efficient with the computer waiting for us less than the other way around. I would expect your experience with the hardware you mentioned to be a minor speedup in pure numbers but a major speedup as your brain becomes free from worrying about saving, window management and revisions (assuming you adapt to the changes and like them)

I get the feeling that with mission control and full screen apps, that the UI is incredibly fluid and optimized but I'm running on some faster macs than yours.

Fun times, huh?