From Eric Peterson at JupiterResearch:

Yesterday Coremetrics released data collected via their LIVEmark Index that continues to validate what we've been saying all along about cookies. By examining growth in the number of "anonymous visitors" being tracked by their customer base, Coremetrics is able to look firsthand at third-party cookie blocking. Add this to our matrix of risks to cookies (originally described here) and you'll continue to see risks to cookie-based measurement plaguing marketing efforts.