PB has larger VRAM amount. so yes the 9550 is technically better than the 5200 but it is choked by the 32MB of VRAM so it can't excel beyond the 5200.
PB is a better option if u r going to "desktop" your system when at home or the office, in particular bc of the VRAM being split between the notebook's monitor and the external monitor. that said i haven't really had any issues w/my iBook set up that way.
i actually like the iBook KB, but many seem to prefer the PBs' KBs.
yes the PB will dent easier. the iBooks have a better reputation for being more durable.
afaik, heat issues are about the same. for basic needs u won't be disappointed by the iBook. heck, for media editing w/ the iLife suites and even some of the semi-pro apps u won't be disappointed.