I've seen a few ups and downs since the beta subdomain test started. I initially showed a 100% increase - then my subdomain name was changed to my username and I saw a dip below normal levels and a climb up to about a 50% increase. Then subdomains was rolled out to everyone and suddenly I was back to pre-subdomain levels.
However, this too has recovered and I seem to be moving up again and am back at 40-50% increase level.
One concern I have is that part of this increase may be due to google thinking the subdomain is a new site and therefore we get a boost - also the panda alogorithm is refreshed monthly (or at least every six weeks!) - so will this have an adverse effect on my traffic.
At the moment I am happy and I'm fairly optimistic that it will continue to stay steady or rise.
I haven't noticed any change due to the creation of new hubs - although my traffic in the last week has increased - I've published three 'quality' hubs IMHO - not sure if there is a link!