It really all depends on what you are trying to accomplish. I did a 'flyer' campaign for a local website I was promoting a couple years back. I used 'dropcards' that looked like a folded $20 bill. When picked up and opened it just contained the site's url and a quick message.
I paid a few people to drop these at bars throughout the area on busy nights over the course of a couple months. The website in question was quite racy and had a word of mouth quality to it, so in this instance flyers brought enough traffic to jump-start the website and get it going.
However I have also attempted to promote CPA using flyers for a Gas Card offer and had the flyers strategically posted on gas pumps and got next to no response.
In the end it is all about what you are trying to do. In my experience, flyers work for promoting a name or giving information, however they do a pretty crappy job of 'selling' people.