I tend to look at where I am at the table. i.e. if I'm in ate position I'm more likely to bluff with nothing, although if there's already been a few callers I may think twice and if there's been a raise I definately wouldn't.
There's a time and a place and if you pick the right one, you can win online bluff quite a lot. I had one last night on a low limit table. I raised 8 times the BB pre flop and got 1 caller. The flop came high leaving me thinking I was going to lose this as he's probably got at least 1 ace in his hands but bugger it. I bet again (about 15 times BB) and he folded. If he had called I would've checked on the turn and folded if he had bet. | 
