Good idea to use C++ style?

I am writing a bunch of UI classes and right now I am using the "string" class instead of messing up with "char" to do all the string handling stuff. I'll also probably be using some of STL but the problem is that no C programmer will be able to use it (I think). So is it still a good idea to implement some of the C++-only functionality?

If you're writing a load of classes then C programmers won't be able to use it anyway ;)

Use the STL as a base, not as a side-interest when you need it.