Counting on my fingers, I have hub generators on ten of my bikes. My rule of thumb is something like, if I'm going to ride it, it should have lights, and they should be on when I'm riding, and I'm not going to support chemical plants by buying more batteries if I can help it. So I buy cheap old dynamo hubs when they come up on ebay, solder together some cheap LED's, and all my bikes are equipped. I have a couple bikes that don't have generators, and they're fun for short rides... but I don't feel safe without a bright light on the whole time.