Here it is a year later and the concept of an ultra small machine is still hot. I think the mini is not for everybody, but with increasing processors, faster ram, and larger hard drives, all in the same small package, the mini, or something like it, will always have an audience.
When I first started seeing laptops emerge in the '90s, I knew that the idea of a small computer that was portable (and then lightweight at 7-9 lbs.) was going to be an idea that would keep a long time. I think the mini has that type of staying power and could last 10 years and maybe has come close since the cube was basically a prototype to the mini, small and quiet.
Of course something super revolutionary, like an iphone with full mac capabilities, a small foldout keyboard similar to what some PDAs have that fold in three, and some sort of folding display could make laptops and mac minis totally obsolete. I have seen rumors about a folding, or rolling ultra slim display that the Japanese were working on some years ago as a prototype idea and the product was made of silicone. If you could use a super iPhone, and put that and a keyboard that fold up so tiny that you can carry the whole thing in a pocket or purse, and you can put all os x apps on it, then the computing field will probably move to that step.