bordering - 7:10 pm on Jul 30, 2012 (gmt 0)
The need for a mobile website, and people trying to sell mobile websites as just another "You need this..." product are two different things.
Given time all websites will probably move to a fluid HTML5 layout and display well on all screens regardless of size. Until then it might or might not be worth having a separate mobile version, based on what your stats tell you.
I've noticed that a sizeable proportion of my sites' visitors are on mobile devices, and their bounce rate is pretty high. This doesn't surprise me as the sites are pretty difficult to use when scaled down. As the numbers make it appear worthwhile, I've been building a mobile version. I decided to do it with all features and all content, so it's every bit as good as the original. It's been about two hundred hours work so far, almost finished (phew), and the process has forced me to face and address usability issues in a way which will be really useful in future development.