Chris Dibona, head of Google's open source program office, sat down to talk with CNET's Stephen Shankland. In the course of that interview, Chris provided great insight into how Google views open source and contributes back to the various communities from which it derives benefit.
However, it was this response to Stephen's question - "What are the most important open-source projects you ingest?" - that I found fascinating:
The kernel, compilers--GCC, the Python interpreter. Python is very important to us....Java is very important to us, and that's become open-source now. We have some very good Java people working for us....
Once you get past those three projects--the compilers, the languages, the kernel--then you go to the libraries. For us that's OpenSSL, zlib, PCRE. MySQL is hugely important to us. Past that, it starts tapering off pretty quick.
In other words, open-source plumbing matters most to Google. I know that Google uses a range of open-source applications to run its internal operations (some of it public like Puppet, some of it not), but the code that gives Google competitive advantage is plumbing. Open-source plumbing. Everything else is a rounding error.