Well, I sold my 15" TiBook 1Ghz SuperDrive today and bought a new 12" 900mhz combo iBook (also planning on purchasing a G4 with the leftover cash before the summer's out).
I was afraid I might be a little disappointed with the downgrade, but after taking this for a spin, I have no regrets. Given, I don't do a lot with video and only occasionally launch Photoshop, but this things seems just as zippy as my PowerBook while running through my normal daily tasks in OS X (I used the extra RAM from the PowerBook I sold to max the iBook out and plugged in an airport card almost immediately - my impressions are based on this performance).
It also feels much more solid - the build quality seems a bit better - much tighter, no creaking, etc. I actually like the keyboard better too - it sets tigher in the indention and has a more concrete feel - the TiBook keyboard was wobbly. I don't feel like I have to baby this machine or be extra careful handling it (of course, there's a lot less invested in this one!).
AirPort range is amazingly better. The machine runs very cool too. The screen is nice and bright - small enough to be super-portable but just fine for my (young) eyes.
It does run a little warmer than I expected, but I've also been copying four gigabytes of files from the backup drive to get myself in order again.
All in all, I'm impressed. It's not as sleek, sexy, or eye-catching as my old TiBook, but I think it'll meet my needs just as well.
And for bragging rights, a bigger screen, and graphics, I might just buy myself one of the MDD G4s before Apple stops selling them - though right now I'm not sure I'll be needing one.
later,
-blake.