I know this is a little old, but I didn't really pay attention to it as I didn't have an eReader at the time. Using the inbuild browser you can goto;
http://www.portablequest.com/
and play all the old Infocom style text adventure games. I'm not sure if I like it (I find it a little clunky using the virtual keyboard), but still thought I'd share for those who missed this when it was making waves with Kindle users.
Maybe a stylus would make the keyboard better?