The Truth:
The current powerbook 12in is an awesome machine...its a rev E and reliable, it runs software natively, and within reason, is really fast. When I compare my powerbook to other's windows laptops it runs rings around them. However, since my girlfriend got a mbp, it seems slow by comparison, which really does hark to what we will see relatively soon. The issue is though that if your using ilife, surfing, office work, then the current model will be wonderful, it is only if you really need lots of power that the mbp becomes essential.
Biggest assets of powerbook:
Form factor: we don't know whether the new small mbp will be a 12in or 13in widescreen, personally, i'm not a fan of small widescreen displays, and would rather an update of the current form factor (i.e. non widescreen 12in display)
Reliability:It just 'works'
Relative Speed: It is fast as long as you aren't doing too heavy stuff
Biggest assets of mbp (12/13in):
Screen: will be much better in terms of resolution and brightness
Speed: Need I say anything
General: Newer, more future proof machine