Here is someone that has attached his Dell 2405FPW to his 1.33Ghz 12" PowerBook:
http://gathering.tweakers.net/forum/list_message/23028882#23028882
PB12 + 2405FPW + 15" LCD
PB12 + 2405FPW
Which all seems to be working pretty smoothly.
I currently have my 1.5Ghz 12" PB attached to a 22" Iiyama CRT on 1600x1200 and that works pretty good. It can even go up to 2304x1728x60Hz which (besided the 60Hz) works pretty well. Performance over DVI should be even better.
On 1600x1200 + 1024x678 Exposé gets fairly choppy as soon as you have more than approx 8 windows open. Exposé still works really well, you'll just have to do with a 4 frame animation instead of a smooth transition between your normal desktop and side by side windows.
I'm going to see when the DualTone TCO'03 2405FPWs become available and I'm going to order two of those. I we're going to have to wait a few weeks for the TCO'03 version it's probably going to be an order with two Midnight Grey screens. Really curious how I'm going to like these screens when working with photo's...