This is a very interesting discussion.

I have to tell you that I am programming VC++ professionaly for just about 8 months and I am not so experienced as you guys. Moreover I've never used STL...

Yes, portability of code is one reason why you would use STL but my point is that if you're not going to port code to other platforms (e.g. UNIX) is there any reason to use it in a windows app ?
Well, if you also program for Windows using Borland C++ I think you cannot use MFC there... (I haven't touched Borland C++ since version 5.0, so I am not sure)

Anyway, I insist we have to find out if there is considerable efficiency difference between MFC - STL.
But is it true that inheritence in STL is not allowed? I thought this library was meant to be extensible. This is a very serious drawback if it is real.