The counter in the dock shows the same counter as in the top left corner of Usenapp under "Queue".
It shows the total number of items in the queue.
A queue item is created for every subscription that Usenapp checks for new headers.
In other words, if you have 6 subscriptions, the counter will go to 6 and then decrease one for each subscription checked.
Let me know if this is annoying, so I can make it optional.
This dock counter has been added from v 0.80.