Pro 7 vs Pro 8

[Kenackr]

I've been reading a lot of posts lately and noticing that many frequent contributors are using Pro 7 versions and haven't upgraded to Pro 8.

Would someone tell me in plain english what the major differences are OR direct me to where I might find them.

I'm not really looking for a printed list, but more of a users point of view.
The questions are: Are there somethings that 7 can do that 8 can't? What things can 8 do that 7 can't?

In short, if you own pro7 is it worth spending the money for Pro 8?

I have somehow gained the perspective that it probably isn't just the money difference that makes folks stay with 7.