l recently ran an asp.net course for ten people with a pretty even split of delegates - half who wanted to use VB Net and half who wanted C#. I usually let the larger group dictate which language I present in, then the notes and code examples are available in both languages so they can choose whichever they want.
However this time, since it was an even split I decided to present in both languages throughout the course. That may seem like a crazy thing to do, but it just highlighted to me how easy it is to switch - I created a single solution with a mixture of VB and C# projects, then I tiled my windows and typed code in both. One of my training issues is sometimes I go too fast - having to do both languages solved that at a stroke!
I also felt that the delegates got a good appreciation of the languages similarity and differences in a natural and easy way to understand. And it dissolved any mystique that VB coders may have about C# and visa-versa; and just to reassure anyone who is wondering - I covered exactly the same content as I usually do, and got great evals.