We're totally comfortable with things like that. We have different parameters (steering well clear of client conflicts), but we also (a) care very deeply about IP and (b) don't have problems with people doing off-hours work.

My previous employer (Arbor Networks): roughly the same way. People had side/off-hours projects that involved network instrumentation.

I think you're overgeneralizing.

That's important because if you weren't, and virtually all employers would have a problem with these kinds of side projects, the risk/reward for asking permission would be different.