not2easy - 3:08 am on Jan 20, 2013 (gmt 0)
I am not blocking Google and Bing, but I have started adding Googlebot-Image and msn-media to my disallows. I expect it to cut into my traffic, but I think the improved performance for actual visitors is a big plus. BingPreview is blocked by UA because they pull the whole page with css, js and all with no actual visitor. When logs show thousands of GETs a day for non visitors it is not a hard decision.