I've been using a Lenovo X61T for reading fiction and comic books in PDF format. As many have noted, the screen is wonderful for this purpose, especially for comics:
I think comics on the tablet actually often look better than they do in print. However, I agree with Wayspooled and others that it's a bit heavy at 4 pounds, and all of the Windows overhead is far more than I want to deal with for an impulse read. I find that I use the Sony Reader far more often for reading straight fiction. I use it for unconverted PDFs regularly, but in landscape mode to get a comfortable text size.
My ideal machine would be a light, iPhone-/iPod Touch-like tablet equipped with an 8-10" screen with the iPhone's high pixel density (160ppi), the same slick interface and the web-enabled feature set.
More photos and thoughts on the Lenovo X61T here:
Comic Book Fans Surf the Waves of Change
Lenovo X61T Hands-On: A Bookworm’s First Ride
Lenovo X61T: The Reading-on-the-Couch Test)