I find that they are great as a consumption device, or to do quick postings on a forum or such. For anything that I need to create anything, including a longer forum posting or article, they're way too cumbersome of an interface.
For checking out the news or browsing for information - they're quite handy.
I got it primarily to make GPS maps of where I go off roading. Handy little thing for entertainment in the bathroom, too!