We really like Linkedin polls here at dnx! They can be useful on a couple of levels - firstly, using your network to get some insight for a meeting (always good for prospecting and pitching but also kicking of new projects). Secondly, as a cost effective and quick way to pull together some stats for clients around specific subjects. We recently ran a poll on Smartphones and within 3 days had over 1000 responses - the system also gives you a good analysis of responder demographics.
Okay, so this isn't scientific and 100% robust but does give us some good numbers to start the process and help formulate some thoughts, before kicking off full research. And... we all like numbers!
Would be interested in other people's experience of this.