+1, whilst I'm no saint, I've seen some lunatics going so fast in their hatchback/ saloon that they understeer so much and end up completely on the wrong side of the road on a blind bend! Makes me cringe.
I'm happy to give it the beans (not that I get to see any nice metal for some reason), but I don't like doing it in iffy weather and always back off before I need to pull 4th gear, just give them a little taster before they speed by :driving:
If it's in a straight line I don't see the problem in iffy weather, unless it's standing water. Cold is just, well, cold... as long as everything's up to temperature (including the tyres) then no problem. Then again, I came from having a TVR Cerbera so the Z4 is a pussycat in poor conditions in comparison.