fishfinger - 2:46 pm on Jun 5, 2009 (gmt 0)

In Google the AdWords results may account for a sizeable percentage of the clicks.

It's only one example (the only one I have), but the company I used to work for managed an AdWords account and maintained first place a particular client's key term. We also had first place organic for the same term. I once assessed clicks over 6 months.

Based on the impression data from AdWords, both first places got between 70 and 80% of the clicks between them. I'm afraid that I can't remember exactly how this split between organic/paid, but I believe it was along the lines of a 60/40 split.

I stress this is only one term in one niche.