The only problem though, Kati, is PDF viewing -- Adobe's Reader for Pocket PCs and Palms leaves a lot to be desired.
pootp, ebooks aren't the same thing as reference materials (that might be in PDF). You can certainly use a Pocket PC to read them, though, and if you do, consider getting something like
RepliGo, which is a super-lightweight PDF-like tool that also happens to have landscape mode built in. That said, if you have really detailed diagrams, do realize that a 320x240 display isn't going to be top-notch for the application.
As for "real" ebooks, I wholeheartedly recommend PDAs over laptops for the purpose. It's no fun trying to curl up and read with a laptop. The only alternative to a PDA for ebooks is a Tablet PC, and there are notable advantages and disadvantages to that approach.
--janak