ember - 10:19 pm on May 29, 2006 (gmt 0)
We also charge a flat rate, just because it is easiest on us. Put the ad up and then shoot the advertiser an email reminder about renewal 5 months later (our minimum run is for six months). I'd say 60% of our advertisers renew. We base the rate on the previous six months' worth of traffic: number of pageviews x average AdSense clickthrough rate x .30 or whatever is the going rate is for clicks.