Ambient Findability by Peter Morville
Here's a book that's a pretty easy read, and it's very interesting on how people look for information. It also offers lots of tips on how information providers can make their info easier to find.
This book is on Sun's Safari list, so if you can log into that, you can read it for free, and also download pdf chapters. Here's the Safari link. (on-SWAN)
If not, and you'd like to read it, here's the Amazon link.