Oxydada - 4:58 pm on Jun 23, 2010 (gmt 0)
Same thing happened to me: moved to VPS from shared, and traffic coincidentally dropped.
But, this was back in march/april.
I noticed that my new server has a higher response time, and Google crawl data reports that googlebot spends more 'miliseconds' downloading data than before (around 1300 now).
Could be that the reason of traffic dropping? A kind of slow VPS server (my site doesn't seem slow, tho)? Can response time affect rankings?