Alan Rimm-Kaufmann was generous enough to post a recap of his clients’ year-over-year Pay Per Click performance for 2007 vs 2006. Some useful online-retail benchmarks here, including click-throughs [dropping], CPCs [on the rise], conversion rates and ACS [Ad Cost of Sales] ratios. Fun to compare your own results against these soft numbers.

But Alan’s conclusions — “Stores beefing up their sites and shifting budget to the web. Catalogers holding the line. Pure-plays getting more aggressive” — don’t tell the story as well as his opener:

We’re entering the home stretch: Christmas is about six weeks out. For many of our online retail clients, the next month and half of revenue will make or break their year. PPC impressions will soar. CPCs will rise. And SPCs (sales-per-click) will skyrocket.

Measuring CPC costs year over year is a great practice, but it’ll be more telling to tally the increase in ad expense after the season’s over. The view from here shows early signs of a faster and steeper increase in competitor’s keyword bids, tempered by an earlier rise in the conversion rate. Yup, it’s bound to be a fast-paced season.