graeme_p - 5:53 pm on Apr 28, 2011 (gmt 0)
Likely effects IMO:
1) lower CTR
2) higher conversions as a percentage of clicks
3) some benefit to brand from people who preview but do not click
4) higher CPC
As a publisher, assuming that this is extended to publisher adsense, I think 1) and 4) should balance.
It will make the system work better as it will make life slightly harder for publishers with sites with poorly matched ads, and for advertisers who place misleading ads.