I dont think that the amount of internal space is an issue. I am not the type that NEEDS to have 2000 books with me at all times. I have a couple hundred right now and I keep the rest of my books on my computer and on my Dropbox account... and some on my MobleMe iDisk... I take a good look at my books on the Kindle before I go on a trip so I have a couple of books to read so again, not an issue.
Those are my $0.02