I love these things so much. A personal wiki is a personal encyclopedia, basically. I can't speak for all the diffferent programs, but Wikidpad, the one I use, is incredibly easy to use: put brackets around a word and you've got a new article for that word waiting for you to add text. These were first recommended to me by someone on the conculture (constructed culture) Yahoo group, and I'm amazed at how useful the tool is.