Tiddlywiki is shiny, in the same sense a blue LED on a cell phone is shiny: it's one of those things that might or might not be especially useful, but it's really neat to play with.
From a practical standpoint, well, I have this shiny new hammer and I'm in search of a nail. Right now, I'm trying it out as a place to put those little bits of information that I might've put in my PDA before, things like birthday/Christmas gift lists and names of good restaurants. I've downloaded a copy of Tiddlywiki to my hard drive and have a bookmark to it in my web browser. We'll see how well this works, but I have great faith that such an interesting tool must have a useful application somewhere.