From a Mac userWell, I actually just decided to jump ship (if only temporarily) from being a Mac user my entire life, and ordered an iXPS Gen 2 which is to show up around Tuesday. I have been using my Titanium Powerbook G4/667 since October 2001.
First thing I have to say is, the main reason I decided on the Dell over the new PowerBooks, is because of the vastly inferior hardware of the current PowerBook. They have been pushed ot their absolute limits, and will most likely be the very LAST revision of the current chipset/CPU. The G4 used in them is old and obsolete. The next revision is supposed ot be huge, and will most likely have either dual-core G4's with a faster bus and an entirely new motherboard with support for things such as SATA and DDR2 and such (more likely), or a low power version of the upcoming 970GX G5 processor with all the other goodies too (less likely). Either way, they are a big leap ahead of the current dinosaurs.
That said, if you need a laptop NOW, and cannot wait for these revisions (which are rumored to be introduced anywhere from Macworld Paris in September, to Macworld San Francisco in January 2006), then I recommend getting the 700m, which has much more updated hardware.
But, like others have said before, if power is not a concern, you need to figure out which OS you like better, as it is what you will be staring at the entire time. I myself LOVE OS X (especially Tiger), but I needed the power of an iXPS Gen 2, which the PB no longer has as of now. Just my 2 cents! -JB