We are considering adding functionality to our online application which will require the user to upgrade their Flash player from version 9 to version 11. We have measured and found out that almost all our users have Flash player 9 or higher installed, but a surprisingly low number has version 11.
I want to know what users do when confronted with the request to upgrade. Do they simply upgrade or does this form a barrier to use our application?
Does anyone know of any studies or research on this subject? How can I find out or research for myself?
EDIT:
Great answers so far!
Some aditional information to clarify the situation: all our users are private users, not business users, so it doesn't depend on a systems administrator.
also our users will get a message (image below) from the flash player itself, so the application won't run with a lower version of flash.

finally, a large portion of our users are returning customers and they might have saved some work.