Absolutely wonderful, really made my trip to Montreal. The public bike system is such a fantastic, economical way to explore the city. There's so much flexibility in being able to quickly pick up a bike in one location, then drop it off at the next. There are so many bike-friendly paths throughout the city, particularly the ones highlighted on the BIXI maps. Really wish they had this system in NYC (although the city is probably too crowded to make riding as pleasant as it is in Montreal).
I found a free app for my smartphone (Droid) that make the experience even better. The app provided a Google map with all the stations and a live feed of the number of available bikes and docking spaces. Perfect.
The bikes themselves are pretty well constructed. They're easy to ride and adjust, so don't worry if you're no Lance Armstrong. The "basket" and bungee cord in front are perfect for bags and small backpacks.
Just a warning to be cautious of your time. 30 minutes can pass by more quickly than you think! Can be stressful when you're rushed to return the bike, particularly if a station is full or far away... so definitely get the app if you can.