I was perusing G analytics and decided to sort my All Traffic by visit length (lowest to highest) and in just one day counted nearly 50 visits from almost as many different domains that had a visit time of 00:00 , 1 page, and of course a bounce rate of 100%. There were literally over 1000 in the last month driving up our bounce rate and visitor time down unrealistically. ALL listed as /referrals type. Naturally this instantly made me think of PPC spammers (many were from shady sites and parked sites that might carry ads which we buy from some of the cheaper PPC adsites) however a couple were actually from my own other websites! A couple were from G.se, G.de and G.co.il as well as a couple of the other large SEs.
If G is using Bounce rate, time/pages on site, etc. as part of it's ranking algorithm, then this can be an important issue.
Any thoughts what else could be happening to create these? I didn't think GAnalytics tracks spiders and bots in this area. I've temporarily deactivated the PPC campaigns to see if it makes a difference.