The WkiReader is most useful when you don't have ready access to the Web. Mine is usually setting next to my to be read pile of paper books. Once you get used to the screen, it's easy to look up something. Often times it's difficult to stop reading articles.
The other reason I keep the WikiReader handy is so my middle schooler can have ready access to Wikipedia. For various reasons, he's only allowed limited Web access. Having the WikiReader at hand lessens the negative impact of that rule.
The WkiReader has one shortcoming: you can't readily create your own content. I looked into this when I first got my unit. Much to my dismay I learned that you have to have on hand all of the content you're using before you can create the wiki files. It can't be done incrementally. This puts making your own content for the WikiReader outside the reach of almost everyone.
It also means that I'm stuck with the formatting errors in the original content. There are a number of errors in the wiki articles including the pronunciation guides are missing, some accented characters are displayed funny, and some articles are missing chunks of text.
All in all, I'm happy with the performance but not entirely convinced that it was worth the cost.