The program is so successful because it offers flexibility. It's not a substitute for owning a bike. The economics of owning a bike and the quality of a bike you own are both superior, but only if you want to own a bike and all that comes with that.
This is a substitute for short trips by pubic transit, taxi, or walking. I look forward to taking the TTC to work downtown, using a Bixi to run errands from the office during the day, using a Bixi to get to friends and events around downtown after work, then taking the TTC back home again (maybe even after a couple drinks).
Other than the $100 cost, there's no commitment. There's a large commitment associated with a bicycle you own. Too often have I found myself wishing I had my bike because I had too-far-to-walk-but-too-short-to-TTC trips to make and too often have I found myself wishing I didn't have my bike with me because I have to account for it in my plans.
I guess the most important thing to say... I don't think foolishness is much of an explanation for the success of the program in Paris, Lyon, Montreal, Barcelona, Brussels, Rome, and other cities.
I can't wait.