I never used a curve. I jumped from a Pearl to a Tour, which made the differences quite drastic. I changed mainly because I became eligible for a Sprint upgrade (which usually NEVER coincides with needing/wanting a new phone!) and I was wanting more application memory. Also, my Pearl had a bum USB port.
I am still getting used to the Tour, and complain all the time about how bulky and heavy it is. I like my phone in my pocket (as opposed to a holster, etc.) and after 3 years of a tiny/weightless Pearl, I can barely walk straight with the Tour!
It probably wouldn't be so drastic if coming off of a Curve.
Personally though, if I had it to do again, I would wait.
I've had misery with trackball glitches (2 units), and finally said the heck with it and went ahead and replaced my trackball with one of my old Pearl trackballs. (I haven't had an issues since.)
I'd keep the Curve for another 6 mos or so and wait for hardware and software bugs to weed out a bit.
Oh! If I could get an 8900, I would have gone that route for sure I think.
(** I wish they would have made a Pearl with more app memory!! haha... oh-well...)