In regards to AV Comparatives, I responded to why their tests aren't relevant in in the real world here: http://news.ycombinator.com/item?id=1284321. The bottom line is that detection rates as high as 97% are generally regarded by industry experts as inflated (John Viega says in one of his books that some people estimate actual detection rates to be around 30%). AV companies themselves would never use that number as a part of their marketing campaigns. You'll note that on the product pages of the AV products tested, the numbers aren't listed. If a 99.6% detection rate was actually. valid, don't you think it would be displayed in large and bold letters on the product page?
I'm not saying people shouldn't run AV, but we need to be honest about the actual capabilities of these products. Even if actual detection is only 30%, 30% is better than 0%.