I imagine they (Google) doesn't consider this information private so here's the bulk of an email I got listing prep material and topics: http://pastebin.com/iXGzfkBL
Yep, I got a very similar e-mail before the on-site. There was some more in some e-mails before the phone interviews, like links to man pages, some (public on YouTube) Google videos, and some sample coding problems.
FWIW, I bought "Programming Pearls (2nd Edition)" and "Advanced Programming in the UNIX Environment (3rd edition)". "Programming Pearls" was definitely a good choice.
My problem with APUE is that it includes so much detail about platforms I'm not likely to be exposed to. It's probably a great reference for that stuff (it's almost a rosetta stone for unix programming), but it could probably be half as long without the "extraneous" stuff.
Edit: To clarify, this is for SE, not SRE.