I have tried to like the onscreen iPad keyboard, but I can't do it. I hate the damn thing. One of my readers suggested the Zagg case, but at the time they didn't have one for the iPad 2. Now they do, and I bought one because I'm about to travel. I read this review, which is comprehensive and covers most of what I'd say. My readers know I'm overly gadgeted, and I can't make a case for needing the case, but the last time I traveled I took only the iPad and it SUCKED. It seemed like overkill to take both an iPad and an Air, but I "need" either an iPad or a Kindle for reading. I love my Air, but with a keyboard the iPad actually stands in very well for a production machine, and with this case it's practical. I had an Apple bluetooth keyboard previously that I didn't use because it wasn't practical.
By "practical" I mean the case is skinny and just snaps right on the front. Snaps right off. Slips right into my Timbuk2 bag. Connects easily via bluetooth. The keyboard does not appear to be full size, but it's full enough for me; I immediately set the iPad in the groove and started typing with no fumbling whatsoever. It also has handy shortcut keys for home, search, etc., as well as music control buttons.
I'm a happy customer. Is it worth $100? If you've got the $100 I'd say yeah. It makes the iPad about 1000% more useful. It's been my go-to consumption device, but now it can also be used for production, and I do a fair bit of writing.