I've seen of useful, or useful looking books about Solaris system performance tuning - most of them printed by SUN. I've found the course material of HP Education quite useful. System performance tuning is hard, and system specific. I would distrust any book that claims to discuss system performance tuning without focussing on a specific OS. I'd also distrust any "cookbook".

Go for something that spends a lot of time analysing performance problems, that discusses performance measuring tools (like glance for HP-UX), and goes into detail explaining how the system works.

Abigail