Any good piece of software will be written using many of the principles of OOP, whether you use classes (C++), objects (Pascal), or whatever they're called in other languages. Namely, isolation, modularization, black-box functionality, et cetera.
Some of the popular C libraries (as in not-using-classes-and-not-C++) are even object-oriented by nature - most library calls include a "context" of one form or another as one of their parameters. Guess what? That's the same way classes work, syntactic sugar aside.
People that I've seen fight fiercely against OOP have almost never had a formal programming education, often don't realize they're using using OOP concepts themselves, and have this totally flawed view that OOP code means "bloated and slow", based on observations of really bad code and really old and bad compilers... or compilers in debug/non-optimization mode.
Crappy textbooks and "teach yourself language <lang> in <quantity> <timeunits>" pieces of crap are to blame too, talking about cars, fruits, and animals. For good OOP (C++ biased), you'll need Meyers, Dewhurst, Sutter, Alexandrescu books, as well as the Design Patterns (GoF) book. That's the Real Deal.