I'm going to clarify some things that a few people are making assumptions about.
The reasons that I 'changed my mind' were that there were a few things mentioned on the first date that rang little alarm bells, but due to the fact that there were 'sparks' I was a bit stupid and pushed them to the back of my mind, then I accepted a very vague invitation to another date. There was no date, time, or event specified.
Over the next few days, without the influence of the sparks, the alarm bells got a bit louder and I realised it would not be a good idea to pursue a relationship. This man was definitely interested in a romantic relationship, not a friendship, he made that clear. I did ask in the e-mail if he still wanted to possibly stay in touch as friends, he declined.
My options were to let him down over e-mail, or let him down in person after he had made the effort to meet me and possibly got his hopes up for a third date.
I think I agree with some PPs that dating has slightly different etiquette parameters, in my mind anyway. A 'date' is never just another social engagement in the early days. You aren't meeting up for the sake of the movie or the food, most of us have friends for that, you're meeting up to see if you like each other enough to possibly enter into a romantic relationship and each further date is a step towards that.
I see that this differs from very traditional etiquette, but I know I'd hate it if someone went on a date with me out of a sense of obligation so I think I'll probably stick with my 'do as you would be done by' approach. Actually, I'll just remember in future to give myself 24 hours thinking time before agreeing to a second date!
To Betty Draper, I appreciate that you are stating the case for very strict traditional etiquette, I did not appreciate you calling me 'gauche', 'immature' and suggesting that my behaviour was contributing to my single status, I feel the things you called me were far more insulting than this man calling me 'disingenuous' and this is supposed to be a forum dedicated to politeness.