BES market share, and typical IT Policies

Does anyone have any statistics, even vague or anecdotal, regarding what percentage of BlackBerry users access services via BES?  And for those users, are there any "typical" BES configurations regarding restricting end user installation of third party applications and access to network services by those applications?  Lastly, how do these statistics vary by carrier (Nextel/Verizon/TMobile/Cingular)?  I am only interested these statistics for the newer BlackBerry models (7000 series).  Also, i am only concerned about the US market (not international).

I ask because I am developing a consumer application for the BlackBerry (which needs network access) and am trying to understand what percentage of BlackBerry end users will be able to install and use my application without modifications to their BES configuration (which of course may not be possible).

For example, if 80% of BB users are prevented from installing or using their own third-party network-enabled applications due to BES IT policies, then the market for my application is much smaller.  If the numberis 20% or 60%, the story is of course different.

Thanks in advance!