Just as Perl is the swiss army chainsaw of languages, Apache is the swiss army chainsaw of webservers. You can do just about anything with it, but as a result it's also very easy to cut off your own feet.

IIS is more narrowly defined in its capabilities, but it serves its narrower purposes very very well (so I hear). It's more analogous to Visual Basic: very easy to use and certainly capable, but with many restrictions on the more fancy complex stuff.

Just my $0.02