Most important: in-citing biking is *really* different from the suburbs. I'm used to having to assume that all cars are actively malicious, but there are a hell of a lot *more* of them here. The result is that biking is very different, with less opening up and more paying very active attention to everything around me. Riding in a *predictable* way seems key to safety -- not surprising the cars appears to be essential to being safe.
Trying to find consensus about the appropriate rules of the road for bicycles seems to be futile. My usual rule is "drive like the other people do", and I was figuring on doing the same with biking, but the other people are completely inconsistent. (Especially with regard to red lights.) So I'm gravitating towards what seems to be a sensible middle ground -- either I am on the bicycle, in which case I think of myself as a car, or I'm walking it, in which case I think of myself as a pedestrian. Switching back and forth is acceptable, but keeping the clear distinction seems to be safest.
Hubway as a service works smoothly and well, and I think it's a great idea, but mostly it's driving home that I need to get my own bike repaired. The thing is, while there are now Hubway stations in Somerville, they're mostly about five blocks from where I need to be. There's one in Ball Square, but it's the other end of Ball, so it's still a ten minute walk to get there. There's one near Porter, but still several blocks from Shaw's. The result is that I'm not actually saving much *time* bicycling, although I'm getting a bit of nice variation in my exercise. With my own bicycle, it would actually be a major time savings to bike instead of walking, and I'd be more likely to really do it regularly.
The Hubway technology is clever in a host of ways. I had only one snag (they don't make it very obvious that you need a new PIN every time you rent, which led to some confusion on my part), but making all relevant info available online is great. There's even a very nice smartphone app that shows all local stations on a map, so that you can track exactly where you need to go to drop it off.
Folks have remarked that the Hubway bikes are kind of bulky and heavy, and that's true but doesn't matter much -- for in-city use, having a super-light road bike just isn't as important. They do seem to be very sturdy and solid, are well-maintained, and have a lot of smart details. (For instance, it only took me about 30 seconds to figure out how to adjust the seat, and then I realized that the seat height is marked so that you can choose your bike based on that.) My only real complaint about the bikes is that, even for in-city use, three speeds is kind of dinky, especially since first gear is so low that it's not useful for anything except hill-climbing. But the shifter is easy to use and reliable, and the bikes didn't give me any trouble.
Overall, Hubway seems to be a Very Good Thing, and I recommend it to anybody who doesn't want to have their own bike -- it's a convenient and healthy supplement to the subway system. But I think I'm going to bring my own bike to Wheelworks and get a couple of years of neglect repaired...