Not that I would encourage it, but I think that you can pirate basically any book on the Internet using certain p2p technologies and even direct download systems. Of course nobody would be allowed to link to any of that stuff from here.
In terms of it being absolutely the best e-reader device, I would of course recommend that Archos try to get a Pixel Qi LCD screen on there as soon as there is one at 4.8" and 800x480 that would become available.
Although 6" and 8" e-ink readers have larger screens, I think the pocketability of 4.8" Archos outweights those larger screens and that these good looking Android e-reader software should display the e-books optimally on the screen.
Having the e-reader always in your pocket, obviously, easy to use 3G, preferably with a 3G SIM card built-in in my taste, would of course be best, since you would just pull it out the pocket and load RSS feeds, articles, http://fastflip.google.com
type of interfaces, e-books, and even colorful digital magazines.
I don't think I would read full books using Archos backlit LCD, even with night mode or with turning down the backlight intensity. Though if Archos can get to use a Pixel Qi screen in the next few months, I am pretty sure this could be pretty much perfection.
Android apps would also enable the most awesome systems to manage collaborative annotations using a stylus or fingers, using something like SideWiki to share annotations for any text on the whole web and to use something like Google Wave to collaborate in editing any type of documents.