It looks like things are picking up on the development front with regards to Windows Phone 7 Series. Appcelerator, a company that makes cross platform development tools for mobile systems, recently polled developers on WP7S.
Appcelerator polled 1,028 developers in January to see what operating systems they were interested in developing for. In January 13% expressed an interest in Windows Phone development. The same group was polled gain in March and the good news is that interest in Windows Phone development almost tripled, increasing to 34%.
The bad news is that the Windows Phone is still trailing behind Apple, Android, and RIM systems.
Still the news is encouraging. The March poll was conducted on the heels of the MIX10 Conference where developers learned more about WP7S development. Microsoft has recently released a Developer Training Kit which will increase the exposure of WP7S and might boost these numbers further. You can find the full survey report here.