My site is developed in C# too and I have others to come. Your product I recognize as a superior, but I wish to maintain a 100% C# platform for my present and future ecommerce web developments, I also make recos to other developers. I have used both VB heavily in the past and C# currently and find myself simply "liking" C# better. The constructs, incremeting variables, compression of multiple statements, the syntax .... It just seems to meld better with projects with SQL databases in the background (but that's my opinion). If your product was written in C# this would be a no-brainer.
Also as Microsoft has finally gotten things "right" with Visual Studio 2008, the ASP.NET 3.5 is just great for me as developer in the coming years. After some 10 years I finally have a VS that works right for me.
Your comments in keeping your product in one language are well taken and not taken lightly. However my instinct is that C# will begin to begin to gather steam, particularly as new developers coming out of the schools here in the USA, India, China are among those hooked on C.