I've already shown some examples of double trouble. In her excellent new book "Code Generation in Microsoft.NET", Kathleen Dollard points out that VB and C# have slightly different views of the division operation. VB uses the \ operator for integer division, and the / operator for floating-point division. C#, on the other hand, overloads the / operator to mean either integer or floating-point division depending on the type of the numbers being divided.
So the following VB code produces the intuitive result of 0.6666 recurring.
Whereas the equivalent C# code (shown below) produces the non-intuitive result of 0.
But if you change the C# code very slightly (shown below) to tell the compiler that it's not dealing with integers, then you can produce the more intuitive result of 0.6666 recurring.