I'm wondering the same thing myself. I have a Pearl now, but just ordered the 8700g online last night. I had a 7100 before this Pearl (my second one to have) and I have to admit, I do miss the full keyboard. I am a constant emailer, and I find that the larger keyboard is easier to use. But they both have so many pros and cons, you just have to figure out which one feature you like the most.

Pearl Pros:
Expandable memory
Smaller size (easier to fit in pocket)
Trackball (though some don't care for it)
Media apps (camera, media player, etc)
OS supported by RIM after last OS release

8700g Pros:
Full keyboard
Much more durable (from what I've heard and seen from my Pearls)
Click wheel
Larger screen