I created a WP7 app that utilizes Microsoft Pubcenter. My eCPM fluctuates between $0.90 and $1.00. When I first released the app, about a year ago, my eCPM was

I created a WP7 app that utilizes Microsoft Pubcenter. My eCPM fluctuates between $0.90 and $1.00. When I first released the app, about a year ago, my eCPM was much lower (around $0.25).