Normally, I run multiple ads until I have a tested winner and then stick with just that one ad.
However, I'm wondering if two ads make more sense (especially on the content network). This way if a person comes to a site and doesn't respond to the first ad, there is at least another chance to get them on their next visit with a different piece of creative.
AussieWebmaster, that's a great suggestion. Any reason you picked 25%?
It would be great if Google would let you set percentages for showing different ads. This one at 10%, this one at 90%, etc.