Total surfing is up at Hit Bandit, and the number of websites in rotation has gone down. These two factors mean you are getting many more hits to your websites every day, and more traffic means more signups for you.
There has been a lot of chatter about cheaters being caught at various other Traffic Exchanges recently. Many of these cheaters were banned from Hit Bandit a long time ago, and various measures have been taken to prevent the cheating that they do, including a sharpening of the "Suspicious User Mechanism" that keeps track of abnormal behaviour by members - too much abnormal behaviour and the member's account gets blocked.
In recent months just a few new accounts have been blocked by this mechanism. On the assumption that these people are just "testing the waters" I unblocked each of these accounts, and none of them have turned into repeat offenders.
So not only are you getting more traffic, you are getting cleaner traffic.