From our experience they will give you the odd enquiry. Some of our clients were making a wee bit from twitter but that was all due to the peak publicity a month or so ago.
Twitter is working well for some of our clients but this is more as a tool for information dissemination. We have one client who could be making a lot of money from twitter for his products and special offers but that's another story. I'll post about it later.
Facebook we've found to be completely usesless right accross the board. Maybe we've not explored it enough but the interface we find to be extremely cumbersome, slow and painful to use. We sent our a questionaire to clients and the overwhelming consesus was that it's a waste of time.
Twitter has potantial if you're in the right market - FMCG type sites will win out of this on the sales front. Information sharing is good for saving money or disseminating info amogst the follower base.
We've tried hard at it but it's not something that will benefit the broad business spectrum. There will be winners doubtless and the early adopters will find ways to be at the top of the pyramid. Someone will find a niche that will be exploited then it will be shut down by the twitter gods.
There's some advertising starting to creep in -
Twitter Starts Serving Ads For Third Party Apps (But They Aren’t Charging For Them)