I've had my 15" Powerbook for under a week right now. Here are my first thoughts about it.
External: The Powerbook looks very slick, I like the metal casing. It's certainly lighter than one would expect. I'm a bit mixed on the placement of the USB ports - one on the left side and one on the right side. My Sony camcorder comes with a docking station that plugs into both Firewire and USB, so I am pretty much stuck to using one side there without having wires going all over the place. I have not tried unplugging the USB side to see if the camcorder will still do everything I want it to do (I'll be using it as a webcam in applications outside of iChat), but it is something I will have to try. The Powerbook uses a touchpad for the mouse along with just the one button. Most of my time has been spent in a Windows and Linux world - two buttons has made things easier. I understand Apple's reasoning for just one button, but it actually makes things more difficult for me. I'm going to look into getting a regular mouse - not only to have two buttons, but because I don't care for touchpads - I much prefer the eraser nubs, or whatever you want to call them.
OS X and applications - As I've stated, most of my experience is in Windows (used mostly at work) and Linux (used at home), so there is a learning curve at getting used to OS X. Some of the nuances for me - Zoom: I want my windows to fill the screen, not just grow a little bit - there is not much of a difference between a zoomed and unzoomed window, making it near worthless. The "X" button on a window: If I close all windows of a program, I want that program to quit and leave memory. I do not want to select the program from the title bar and select quit - that's more work than necessary. I do not want to press control and do a button click for a contextual menu, especially if I am using a touchpad to navigate - this is more difficult and time consuming than the right click of a mouse. Printers: I cannot get my Samsung ML-1430 laser printer to work - Apple does not acknowledge Samsung as a printer brand, the Gimp-Print drivers I saw for other Samsungs did not work, and the last Mac driver on Samsung's site states that it is for OS 10.3, not the 10.4 that I am on. Camcorder: Just plugged it in and it worked perfectly.
Safari - Tried it, but I love Firefox too much.
Screensavers: Oooooh pretty!
iChat - Worked just fine with my AIM account, including using my camcorder as a webcam. I would've liked for them to include more IM protocols, though.
I still have a lot to try out, including iMovie and iDVD, the big reasons why I went with the Powerbook. I'll review those, along with further thoughts on OS X as I play with it, in the future.