They're very common — to the point that I wouldn't bother to check in advance. This will be especially true for longer exposures, as the sensor heats up. So, I just assume they're likely and plan to run the built-in pixel mapping function if I notice any.

Or, if I were to shoot RAW all the time, I'd wouldn't worry about it at all, since most RAW converters have their own feature (usually, automatic and on by default) to map out stuck pixels. If your preferred converter happens to not have this feature, you could use Pixel Fixer on your RAW files.)

Since I do shoot in JPEG, if I'm buying a camera that doesn't have pixel mapping as a user-accessible feature, I make sure I've planned for the possibility of a couple of weeks turn-around from a repair center. (I know Olympus and Pentax cameras have the feature; not sure of any others. There's a common belief that Canon cameras do it when cleaning the sensor, but this has been debunked as a myth.)

A lit-up hot pixel can be distracting and annoying, but once mapped out, the impact is something less than a 0.0001% loss of resolution.