The Powerbook does not have separate ram for the video, as far as I know, and I know a lot.
The last revisions of the iBook the 12" 1.33 and the 14" 1.42ghz came with the more modern features that we expect on laptops these days.
So did the 12" Powerbook 1.5ghz/15" and 17" Powerbook 1.67ghz with DDR2 ram.
Such as USB 2.0/Bluetooth 2.0/Sudden Motion Sensor etc. These are features lacking in the previous generations, though some Powerbook lines might have had a feature or two previous to the final revisions.
The last revisions of the iBook came with 512 ram BUILT IN on the logic board. This makes the 12" iBook in some ways a faster computer than the final revision 12" Powerbook that only has 256mb ram built in on the logic board. Both only have one ram slot, so the iBOok maxes out at 1.5gbs of ram, the PB at only 1.25gbs. It makes a difference.
When choosing between the two, I usually went for the Powerbook if I needed it to suffice as a desktop computer at times because the Powerbook has 64mb of video ram DVI while the iBooks only have 32mb of video ram through VGA connections.
That was usually the deal breaker for me. But if you want a great 12" laptop, really the iBook is faster and upgradable just as much as the 12" Powerbook if you don't need the video ram. In my estimation the ram bump in the iBooks makes up for the paltry CPU loss of 1.33 compared to 1.5ghz in the Powerbook.
In order to run Powerbooks or any PPC Mac today, you have to install the right codec for Flash, it's something like 10.1 something.
Runs it decent.
I own the final 15" Powerbook 1.67 with DDR2 ram and a 250gb hard drive, with the High Res screen and 128mb v ram. I can run my 30" Apple Cinema Display off of it.
It's fast enough, the screen is large enough for me and it's perfectly fine.
It has all the more modern ports -- for example with the iPhone you do need a 2.0 usb etc.
Only limit is iLife 09 is final iLife you can install and Leopard of course.