My ThinkPad
I use a ThinkPad T40p, which has a 1400 x 1050 resolution on a 14.1 inch LCD. It may seem a little high for a 14 inch screen, but when surfing the web or using Excel it works very well. I do adjust the Windows icons and menu fonts to a larger size, but other than that it's actually hard to go back to a 1024 x 768 screen.
My sister uses the 15 inch TiBook. The 15 inch's screen is defintely brighter and is more clear than mine. It's also a widescreen which makes it more useful for DVD playback and video editing. However, I find that it's actually a little easier to do word processing and other office related tasks on my ThinkPad. When using MS Word on the TiBook, it seems as though I'm wasting half of the screen, where as with the ThinkPad, I can use the full screen and see more vertically without sacrificing font size.
However, the wide screen does allow me to use another program and see both programs opened at the same time, which make it much easier to drag and drop files into or from Word.
Finally, my sister's TiBook has Keynote installed. This is far more superior presentation program than PowerPoint. It offers better quality transitions unseen. I wish Apple would come out with one for PCs, but then I'm beginning to wonder why I haven't bought a Mac yet!