I have noticed that revenue per click on PPC type ads may tend to be seasonal.

I have a small web site which started in late October 2007 that just can't get past a PR rating of zero, so I've stopped trying and focused on quality posts.

Well, for much of the winter I was averaging say between $0.15 and $0.50 per click.

Then all of a sudden the past two weeks the average has been steadily and quickly going up to between $0.50 and $0.75. Then yesterdaay I averaged $.90 on a day that I had the most clicks ever.

It think seasonality plays a factor with rate per click. My site deals with home renovations and in North America we are just about to or have just started, depending what part of the continent one is on, the spring home renovation season which is the prime activity. So, I am thinking that building supply retailers and distributors are willing to pay more for their ads to appear.

Hope that helps!