Well, I'm certainly using it—I've offered a bit over 150 bounties (>90% of them on other people's questions). Other users have offered a substantial number of bounties as well. I'd say it's somewhat effective, but better questions are more effective.
However, most of my bounties have been to reward good answers rather than to draw attention. A number of users have offered many bounties on their own questions (in several cases, almost all of their earned reputation has plowed back into bounties) -- those users clearly seem to see some value in doing so, whether it's to gain more / better answers or simply to reward the people who spend time on their questions.
(I haven't examined the figures in any detail so these are just seat-of-the-pants impressions.)
Of the draw-attention kind, my rough guess would be that I had something under a 50% hit rate (drawing at least a somewhat helpful answer), and I'd say that if the question was a bit unclear before a bounty, it will remain so after a bounty is placed; the rate could be much lower on the questions that weren't really clear.
There also seems to be a good deal of variation in hit rate by topic.
Overall, the best thing you can do to get attention for a post is make it as clear and engaging as you can. Only after that would I suggest you consider a bounty, but with a really good question you should still be prepared for the substantial possibility of getting no response.
On the other hand, offering bounties does seem to increase the upvotes a question gets, sometimes to the extent that it's worth a substantial fraction of the bounty, so if the question is a good one and you bounty it yourself, sometimes a good fraction of the bounty cost is made up for. If you bounty good questions it's not necessarily very expensive.
You can get statistics from the Stack Exchange data explorer for our site (this one will let you choose a site)—if there's no existing query that suits your needs, you may be able to write one; there's a tutorial on writing queries for it here.
Here are a few existing queries that may help you some: