I actually did a similar mod to my powerbook, (500mhz, not sure what this one was). A couple notable differences: I just used sandpaper on the whole thing, which left a nice subtle brushed pattern on the case. I also did the entire case, not just the lid, and what this mod misses is my favorite part: the bezel is black (magnesium?) so you get a great two-tone effect (rather than two mismatched shades of grey, you get a nice matte black surrounding the metallic titanium). Lastly, to top it off I put a couple layers of black plastic (thank you Glad Garbage Bags) underneath the Apple on the back, so it now glows black (matching the sides). I love my PB, I think this is a great simple mod that just requires a little patience (gotta be careful of the apple, the trackpad, and a couple other little delicates. Also beware bending the screen, the metal is really thin). As an earlier poster said, no worries about corrosion since Ti is barely reactive. Fingerprints do show up, and the titanium loses its luster quite quickly. It goes from a brilliant silver to much duller in about a week. A quick once-over with sandpaper will make it nice and shiny again if you've got company visiting, but for the most part just using paper towels and water will wipe away the grease from your hands and keep the PB looking respectable.
You might try using magic eraser to repolish your ti when it loses its luster