The TiBook screens are indeed quite nice. I still get adoring comments about mine. If you end up getting one, you'll want to invest in a screen protector for it so that it doesn't get marred by the keyboard when the laptop is closed.
Secondly - and this comes after three years with my 800mhz tibook - it's really not that sturdy. I try to take pretty good care of it, but it's my primary machine and I'm a contractor, so it moves a lot with me. The frame has always had a lot of flex, and this results in some of the parts not quite fitting perfectly with each other after so long. It's actually been back to apple twice - once to replace the screen, and once to replace the motherboard. It seems possible to me that the mobo failure was caused by the inner frame just not being strong enough and the whole thing flexing when it really shouldn't. I wouldn't buy a used three-year-old TiBook unless I could look at it pre-purchase and see that it had sat on a desk for that entire time.
As far as the ibook goes, they're rock-solid. My sister has had hers - a 500mhz i believe - for almost 4 years now, and she treats it terribly, and it just soldiers on. In terms of physical reliability the iBook is in a totally different class than the TiBook.
As far as speed goes, it does a good job, I guess. I've got a gig of memory (it came with 512, and the extra made a pretty good difference) and a faster/bigger/better hard drive than the original, and can do lots with it. Pages is pretty slow as soon as there are images in the document. FCP works well for editing, but rendering is an overnight task - though it sounds like you won't be doing that kind of stuff. It's starting to frustrate me a little when I open a new browser window in mail and it takes a couple seconds to come up. I'm installing Tiger today to hopefully get another bit of zip out of it - will let you know how it turns out.
They should've called this the PanzerBook.