All advertising is currently handled through
Project Wonderful.
Basically the adspace is auctioned. You get your ad on the page the instant you agree to pay more than everyone else. You basically pay per minute (I don't know exactly how often they take money from you), and you pay such an amount that in 24 hours you pay the amount you agreed to pay.
So if you agree to pay 24 dollars per day, you pay 1 dollar every hour.
If someone outbids you, the counter instantly stops and you wont lose any more money.
To get a better explanation how it works, you can read
this.
To see the current price and/or place a bid, just click the box below the adspace you want to advertise on, and follow the instructions. These pages also show statistics about my visitor counts and incoming links (links from search engines are filtered out), along with average costs in the past days.
When you bid for the first time, I'll have to approve the ad before it is shown on the page. After your bids has been approved once, any new bids by you will be approved automatically.
The obvious down side of this whole thing of course is that you can never be 100% sure that your ad will be shown on the page.
I choose to only accept ads that I think are appropriate. I accept mature, but usally not sexual content. Also I might reject your ad if it has horrible colors or is very low quality.