Colonel who?

Best book to read up on modern OSs? Ideally, I'd come out knowing how to hack on linux.

http://www.amazon.com/Solaris-Internals-OpenSolaris-Kernel-Architecture/dp/0131482092/

Linux for hackers

http://www.kali.org/

http://plan9.bell-labs.com/sources/plan9/sys/src/

>>3
No, that's linux for crackers.

>>4
But but... the creators of plan 9 don't even use it themselves anymore..

If you want to read up about modern OS's all you should do is read the manpages on your system.
Why?
Because according to RIMMUS and GNU/g/ an operating system is nothing but userspace applications with a kernel tacked on.

>>5
It doesn't matter of they use it or not if you can use it to learn about modern system. Learning about one system can help you appreciate the difference in other systems and Plan 9 is an excellent system to learn because it's full function and yet, the code is very clear.