Since some say that virtual method calls are evil, I ran some tests to check how much overhead they create in C#.
Unchecked result: They are about 5 times slower than nonvirtual calls. However, before you get overly excited: On my machine I could still make 5 Million virtual calls in 0.04 milliseconds.
I guess in most cases the time spent in virtual calls will still be insignificant.
Addendum, for those who shy away from indirections: There’s no measurable penalty for nonvirtual calls (compared to inline code)