I'm a verbatim guy myself.
I think first thing to try here is to use a higher quality type of Media (ie NOT Memorex.) If, after that, you consistently burn more successful DVDs, you'll know that that was the issue. If you're using a top notch brand and you're still getting a lot of coasters, then it's something else.
Another thing to try with your current brand is to burn at 1x or 2x speeds instead of your maximum speed and see if that reduces the fail rate.