They're now my preferred fermenter by far. If anything, simply from a safety point of view... I had read too many horror stories about glass carboys shattering for no reason. The BBs are just so easy to lift, sanitize, etc., and the neck is larger as well, which makes dry-hopping and adding secondary ingredients that much easier. Also, they're just about as oxygen-impermeable as glass.
The only time I get a little frustrated with them is during cleaning, since you can't use a carboy brush. However, now I just add about 1 gallon of very warm water, the appropriate amount of cleaner, and turn upside-down with a stopper in, in the sink, let sit for 20 minutes, and then stuff a washcloth in it and swirl it around. That's been working very well lately.