I got manual because I wanted something fun. I've been driving an automatic 1984 Honda for the last 8 years, so I figured it was time for a change. I drove a manual transmission Isuzu before that, so I still remembered how to drive one.
The Mustang was actually _really_ easy to get up to speed on. The only weird thing is having to push down on the stick to put it in reverse.
I think, as I get used to it more I'll get better mileage, but mine currently reads 16.2 MPG.