Don't have exact numbers for you but hopefully these stats will help:

<a href="http://windowsteamblog.com/ie/b/ie/archive/2012/04/30/continued-growth-for-internet-explorer-9-on-windows-7.aspx" rel="nofollow">http://windowsteamblog.com/ie/b/ie/archive/2012/04/30/continued-growth-for-internet-explorer-9-on-windows-7.aspx</a>

I'm pretty positive it's not a small number and worth supporting.