The major differences are the buildin mic and newer LCD technology. Oh, and the "hottest feature: reduced battery life", according to Jim Sterling at Destructoid.com. From the pictures shown below, whether the new LCD would justify the shorten battery life (20-30 min) is up for you to decide. I personally prefer the PSP-3000 model. 
Front view (up 2000; down 3000):
Back view(up 3000; down 2000):
According to Famitsu, the edges of PSP-3000 fit your hands better when holding it.
LCD Spec (2000 vs 3000):
Size 4.3 inch (both)
Resolution 480 X272 (both)
NTSC color gamut 53% 85%
Contrast ratio 400:1 2000:1
Response time 30 ms 8 ms
Anti-glare no yes
Some pictures (up 3000; down 2000)
sources:
http://www.famitsu.com/game/news/1217756_1124.html
http://gnn.gamer.com.tw/9/32249.html
http://www.jp.playstation.com/info/release/nr_20080902_psp3000.html
It (PS3's market share) might hit 30%, but definently not more. ~ Neo
Flaming (Calling another user (any user) a fanboy is flaming.) ~ Machina-AX
