I have noticed a significant drop of traffic across many of my sites. I have recently moved them to a VPS (with the current traffic they could have stayed on the cheaper Shared Host). There were some other things going on, but I keep wondering if changing hosting companies can show negative effects on rankings? If anything, the average load speed for google bot became 7 times (or more) faster (crawl stats in webmaster tools). The Uptime has also been very good (better than shared) except for one time where I messed up a bit for a couple of hours.