I absolutely love my Kindle. Here's a word of warning though, if you like to read books that have code listings you will need the DX. They just don't work on the 6" screen.

Reading linear books (novels, etc.), get an e-ink reader like the Kindle, etc. You won't mind the page delay if it's one page at a time.

Reading tech books (manuals, reference material, etc.) get an iPad or subnotebook. Much faster to flip rapidly through as there's a much smaller page load delay, better search etc.

I'm so thankful for ebooks - there's a line in one of the perl docs that says "You can't grep dead trees", which has always been my beef with paper docs.

If you read books buy a Kindle or a Nook (Kindle is great especially when you are buying books, but nook gets wonderful reviews as well and supports quite a bit more). If you are going to be reading pdfs an Ipad is the way to go.