Retailers, what % of your PPC to CSE's?

[shorebreak]

Hi all,

I'm trying to get a handle on how much of you retailers' ppc spend is going to

Shopping.com
NexTag
BizRate/Shopzilla
PriceGrabber
MySimon

No need to break it out by the particular Comparison Shopping Engine (CSE), but if you care to comment on what % of ppc is going to the CSE's vs. Google and Overture, I'd appreciate it.

Thanks,

Shorebreak