This is a completely unscientific test, but it is something I've been dealing w/ lately. Thought it might help someone. As the result of a couple of malware flags on some of my sites, I decided I was going to move servers. One of the malware warning pages allowed me to lookup the network my my site was part of and I found that the network was hosting a number of sites that were distributing malware. It didn't seem like anything out of the ordinary for a large shared host, but I was nervous I was going to get a penalty for being associated. I was using host gator's seo hosting setup, so it makes sense that people would be doing some BH stuff on there. So I moved a couple of sites over to Media Temple. Well, a couple days after the move I've seen my traffic and impressions (# of searches my site appears for) jump. I'm not really sure what the primary factors contributing to this increase are, (no malware, better network, better servers, faster loading site, etc.) but it seems like a worthwhile change days afterwards. It seems like its worthwhile to spend the $ for good hosting for your $ sites.