My rule of thumb for OSS software is that if a type of software is integral to developers' jobs, then there are some very good tools available. Operating systems, web servers, text editors, database systems, ... are all good examples of this. If the type of software is not integral to developers' jobs, then there are fewer good alternatives. There are some pretty good ones (OpenOffice, GIMP), but they're often not as polished and lack power features.