After this clearly unsuccessful (according to many) E3, I'm pretty confident they'll have a 50 million units "fad" up to and including FY 2008 - that's in just 2.5 years.
If it were ever to slow down, there are always: price drops, new colors, redesigned models. Meaning? It just won't slow down, not even a bit, not until FY 2009 at the earliest. And after that... it's a stomping train.
100 million is not just possible. Put simply: it's the most likely outcome of this generation.