GCC has nested functions, which most GCC users hate. Clang has blocks, which are at least widely used on OS X at least and proposed for standardization. I'm not sure this is a point in GCC's favor.
As an Objective-C (iOS) developer, I really love blocks. I thought the syntax was kind of weird when starting to learn it, but it's grown on me. I really hope ObjC blocks will become part of the C standard someday. If I remember people have proposed C++ lambdas to become part of the C standard as well. It will be interesting to see which one (if any) will win in a standardising process.
