Never used it I'm afraid. My company is large enough to have in-house IT, and we were tasked installing/running BES. Lots of people in my position use the support that comes with their network (I originally bought my BES from o2 along with devices and contracts, now moved to t-mobile. I don't have t-support so also buy new BES upgrades from t-mobile).
Other (larger?) companies have t-support contracts directly with RIM.

Small companies who don't want the responsibility of buying/running/supporting BES & hardware and the back end mail infrastructure, or who have a small number of devices, would probably just go for a hosted solution.

So, although I think there is a market for what you are doing, I don't know how large it would be.