LOVED Montreal and LOVE, LOVE, LOVED Bixi. It is not the primary reason why I visited, but it is the primary reason why I will visit again. What a great way to enjoy an already lovely city!
I am a huge fan of the concept, and I have used similar bike systems in other cities, but Montreal's Bixi is the first I have seen that has done such a thorough job of laying out their system; there are an adequate number of stations and they are logically located near bike paths so that you can find them in a timely manner to avoid overage charges. I wish every city that installed a bike system would be so logical (u-u-uhhh-um, yes, I'm talking about you, Chicago).
Furthermore, it's not just the Bixi bike system itself, it is the commitment Montreal has made to being a bikeable city that makes the whole thing work. The city has obviously made a real investment in their bike-lane infrastructure and it has created a local bike culture that goes well beyond just the excellent Bixi system. Kudos to you Montreal. I hope the rest of the world is taking notes!