I've bought an iPad today. 16 GB, WiFi. I went for the cheapest model because I already have an iPhone 3G plan and that's enough for me. I'm very happy with the iBooks app, although there's no content available for Canadians in the iBooks store yet
On the other hand, you can easily load DRM-free EPUBs in the iBooks library using iTunes and the books look really nice. Even the Smashwords files look decent in that app.
It's to early for me to say that I'm satisfied with the device itself (I only used it for few hours), I know all its downsides and I'm absolutely NOT an Apple fan, but the iBooks app is in my opinion quite impressive.