I own both
Brought a new 1.5GHZ PB last summer for scriptwriting. It did what I needed it for, and was perfect, as I needed something portable, and big enough to display 2 pages on screen at the same time, and also capable of handling small scale video editing. (for working with tapes of improv sessions)
It's earned its money back.
Then I brought a second hand 700MHZ ibook 12" for my partner (£350), and its actually kinda become my own now 🙂
The 15'' PB is now kinda my home computer, as it's just a bit too big and heavy to move around easily, and when I go travelling, I take the 12'' ibook.
The ibook is perfect for pulling out on London buses and Tubes and trains and in cafes/ coffee shops, it's the right size for my lap. The 15'' PB is too flash and big, I worry that it will attract attention and get stolen. the ibook is much more unobtrusive.
Now, the PB is kinda stuck on my desk, as at any one time it will have a combination of mouse, keyboard, external monitor, mike, printer, webcam, still camera, video camera, ethernet, scanner,power lead, external 300GB drive, or all of them plugged in at the same time (!)
[I have wireless, but sometimes I plug in the ethernet as well for big transfers or modifying the ASDL router/firewall settings...]
I have no regrets about buying the PB; I would have never finished the script without it, and the money I earned from the script paid for it. I'm very happy to own one of the sweetest sexiest laptops in the whole world 🙂
That it does so much on my desktop now is testament to what a good machine it is is, the incredible expansion capablities that Apple laptops have, and it's still capable of pretty heavy video work.
Now, with a decent iMac and Mac Mini available, I would probably go for the cheapest second hand iBook I could find (cheap means less worry about taking it out, having it stolen) plus for a desktop the cheapest that meets your budget/needs from the mac mini/ imac/ powermac range.
cheers
tomato