I am not the most gentle person on notebooks (heck you should see the crack in the case on my Wallstreet from when I dropped it - and it still works!). My 12" PB is holding up very nicely. The finish has dulled a little bit, but most of that will clean up nicely with a damp cloth. The finish will scrach and dent, but I have found it to be very superior to the old plastic PB's. I never got my hands on a Ti Book, though.
The Thinkpad I use at work had a texture molded into the plastic that's been worn smooth on many of the keys and the palm rests. The 12" Albook is probably less sensitive to wear, being metal and all, but you probably will see the finish start to get dull...