My DT sales graph shows a 50% drop in peak 7-day average income from mid-June until the start of August. Since the start of August sales have nearly recovered to their high point. Income in the months of May thru August are within 15% of each other.
(http://www.strathdee.net/temp/dt_sales.jpg)
The bottom line: Sales at DT peaked in June, dipped a bit in July, and are now rebounding in August. During this period I increased my DT portfolio by 387 images (~36%).
Am I happy with DT? No way. Although DT is consistantly "the best of the rest" for me, it only contributes 10%+ to my total income.