The iPad goes beyond being _an_ ebook reader. It becomes all of them.
Turn it into a Kindle for free.
Turn it into a Nook for free.
Read PDFs.
Run Stanza, or any of many other reader software.
Full price or discounted or free, there are way more book sources available on the iPad than you imagine. All wireless.
The iPad goes beyond the need for USB and other media. Physical is passé.
Set up email on it and email the books to yourself. In the next release of the OS (a couple months) a PDF attached to an email will be automatically added to your library. Likewise Word files.
Install the Dropbox app on both iPad and desktop. You get a special folder: anything you put in it appears on your iPad - instant and wireless.
And again, multiple ebook readers will run on the iPad, all getting books wirelessly and without physical media.
BTW: on a tangent, look into portableapps.com asap.
Those of you who are science fiction fans might want to check out the Baen Free Library. They have a ton of their current books online for free. It's a great way to check out new authors without shelling out bucks to do so. I highly recommend the 1632 series. One thing that I think is really cool, is that some of their hardback books come with a CD that contains a bunch of their other books. For instance, we recently bought the latest Honor Harrington novel in hardback, and the CD contained the entire series up to the current book! (of course we already had most of them as dead-tree editions) Most of the books are available in whatever format you like.