[tptacek]

Yep, but the commercial compilers generally had better STLs (particularly for debugging), debuggers that could properly mangle/demangle symbols, and precompiled headers --- in addition to different sets of C++ features that did or didn't work properly.

[saidajigumi]

Largely true, but I recall actually isolating one chunk of code and compiling with g++ just to get halfway sane error messaging around a (IIRC) template-related error. I.e. you could do worse. The primary compiler for that code was the circa-2001 ARM tools suite. I wrote a few novels worth of feedback and bug reporting to them...