My suggestions for AdSense would be to spend $500 at once rather than trickling the money out. This gives Google enough knowledge of your conversion rates that you can switch to pay-per-conversion. Bear in mind that you also have to be ruthless about excluding websites where you aren't going to get any conversions during your pay-per-click period. So track your spend daily and exclude-exclude-exclude sites that don't convert. I don't know if you've done this, but it basically halved our advertising costs and turned us from advertising at a loss into advertising more or less at cost (perhaps profitably assuming word of mouth, etc.).
Thanks for the tip!