BATTERY LIFE
My Panasonic W2 (12" XGA) originally ranged from 5-6 hours for light use to 2.5 hours for watching DVDs at max brightness (more recently it's been getting half that as the battery nears the end of its usable cycles).
However, that is an exceptional battery life for such a lightweight model (2.8 pounds with the optical drive) and Mac laptops seem to be generally on par with PC laptops as far as power consumption and battery watt-hour ratings go. The G4 is not as efficient as the Centrino, but that difference is minor compared to the power requirements for the rest of the laptop's components (LCD size, brightness, hard drive and DVD use, etc).
POWERBOOK DISADVANTAGES
My biggest disappointments with the powerbooks are:
1) Their resolution is too low for the screen size. I can get 12" and 13" 1280x800 Windows laptops (Dell Inspiron 700m and Sony Vaio S-series, for example) and 14" 1400x1050 (Panasonic Y2).
2) The 12" powerbook is heavy. I like small, lightweight laptops and the powerbook weighs 65% more than my W2 while having similar hardware. Even the Y2 with its 14" screen weighs only 3.3 pounds (including optical drive!). While the W2 and Y2 are exceptionally lightweight, both the700m and S-series mentioned above weigh also only 4.2 pounds. On the plus side, the 15" Powerbook is significantly lighter and thinner than most 15" Windows laptops.
SONY S-SERIES, WINDOWS VS OSX
I seriously considered getting the S-series (its XBrite screen is truly stunning), but two things stopped me.
1) Once you add DVDR, a faster CPU, memory, XBrite, etc it's more expensive than the powerbooks (w/ educational pricing).
2) Windows vs OSX. Windows is temperamental in a lot of ways, and wifi and power management are two of them. I've run XPPro on several laptops and I sometimes get disconnected from WAPs for no apparent reason (often requiring me to disable and re-enable wireless to fix... this is with newest wifi drivers and SP2). Then there's hybernate and standby... sometimes they work properly and sometimes they don't. When I open the lid, the Windows laptops I've used will resume from standby in 2-4 seconds 4-out-of-5 times, but that other time it can take 10-20 seconds... and hybernate outright failed to resume so often that I stopped using it. I've never seen an iBook/Powerbook not resume in less than a couple seconds.
ORDERED A POWERBOOK
I decided a couple weeks ago to get a Powerbook for work and held off until the rumored updates were announced. I ordered a 15" 1.5GHz, superdrive, 1GB earlier this week (woulda gone with the 12" if it had backlit keys and was lighter).
6 months ago I had no Macs (even though I'd been itching to play with OSX for years). Since then I've bought an iBook for my wifi an, a G5 iMac for my son (well for me too), two Mac Minis and a Powerbook for work.