I haven't seen this mod in use on a large store yet (biggest I know of are the 2 in the first thread post, for SoundChoiceStore and Leukstewinkel (sp?) )
what you could do, is record page load time, server load, # visitors, etc, in your peak load time, and then switch on the mod, and check the stats again
i think most of the big shops already had a commercial SEO mod installed when XC SEO came out, but it would be nice to have a list of websites that are using the mod.