I use twitter (cliffball), but, all I seem to get is followers, but no hits to my website from it and I'm pretty sure it hasn't helped sales So, I'm still on the fence about it and I joined twitter over a year ago. Maybe I'm doing it wrong, I'm not totally sure.
I have been a registered user of twitter but just recently (last 1 1/2 months) I started using it much more. I have found that my web site has exploded with increased link popularity. Before using it the way I have now my link popularity was around 7,000. It is now over 30,000. The increase in popularity is validated by more than one site which measures link popularity. My search engine exposure has also dramatically increased. I know that just using twitter has not been the only reason but it is the only change in my activities that would account for this increase.
I am a grandparenting examiner for http://bit.ly/1BWGI and twitter has really made my page views jump, got two subscribers and it helped me climb to the #2 spot in my field of examiners for Des Moines, IA. My name on twitter is dragoneggs and yah, join it is great.
We've been using Twitter to market our free, online book-marketing technology called BookBuzzr. It's been working very well for us. About 300 authors have uploaded their book-information and book-extracts into BookBuzzr format. We've got about 2400 followers on our account - @bookbuzzr
But I do need to tell you that the bounce rate from Twitter is quite high.