I'm a speculator, and if mtgox offered leveraged trading, Id probably use it. I wouldn't trust a newer service though.
I'm pretty sure that mtgox isn't going to offer leverage at least in years, they make enough dough with their current business model, and their software seems to be pretty crappy (they can't add new features very easily since it is badly designed).
However if a new service would come, perhaps you could risk a few btc to try the service out? Eg. Test the functionality and that withdrawals are working, then maybe try risking it with higher sums?
