Funny, I too just got a 12" 1.5 GHz 512 MB PowerBook!
As these other chaps have said, the Al PBs are much more solidly built than the Tis. That said, however, I don't think I've seen a 12" Al PB (mine included) that didn't have some slight dents/bent metal around the edges of the bottom case. It seems that while these are leaps & bounds better than the Ti PBs (hinge assembly especially!), they're not without their own, unique concerns. I'm pretty sure that as long as you're even mildly careful about what you go banging your 12" into, it should do just fine!
As these other chaps have said, the Al PBs are much more solidly built than the Tis. That said, however, I don't think I've seen a 12" Al PB (mine included) that didn't have some slight dents/bent metal around the edges of the bottom case. It seems that while these are leaps & bounds better than the Ti PBs (hinge assembly especially!), they're not without their own, unique concerns. I'm pretty sure that as long as you're even mildly careful about what you go banging your 12" into, it should do just fine!