One of my main guitars has a scalloped fret board - I like it so much I'm thinking of getting the rest of my guitars scalloped too. Some of my mates that have tried it didn't take to it at all though: I guess it's either something you love or hate.
Once you get past the fact that your fingers don't come close to touching the fingerboard at all (which does feel a litte weird at first), there are no real negatives, as far as I can tell. Bending and vibrato are so much easier to control, but I wouldn't say it's any faster to play. Well, maybe it is a bit easier to move around.
The only real negative I can see is if you want to get one of your own guitars scalloped. I've talked to Jon at Feline Guitars about it, and he told me it's one of the hardest and most time consuming modifications to make on a guitar. It's not cheep either - he quoted me £240 to do a full 24 fret neck.
At the risk of stating the obvious, it is also an irreversible procedure, so make sure you like the feel of a scalloped board before going out and cutting up your favourite guitar....