We have put a baby seat in the front seat of a two-seater car that didn't have an airbag (that way at least you don't need to worry about whether it's been disabled). That's not really an issue any more since a flash flood wrote off the two-seater.
In general no, wouldn't put one in the front seat of a car otherwise (although I can imagine there might be circumstances where I'd do it as a one-off, just can't imagine what they might be). If I needed a car to fit three child seats in I'd get one that could fit them all in the back.
On a side issue, we used one of those mirror arrangements so that rear-facing DS in the back could be seen in the rearview mirror if driver moved head slightly.