In the past I would have been digging for hours through performance monitor logs looking for interesting spikes or patterns.

Now there's a scripted tool you can run on the logs files while you are off making a coffee:

Performance Analysis of Logs (PAL) Tool

I recommend downloading and watching the hour-long LiveMeeting training (Note: the "Watch Online" link won't work; I'll get that fixed or removed).

Have a look at Clint Huffman's blogs too:

• Pre-June 2009 http://blogs.technet.com/clint_huffman/
• Post-June 2009 http://blogs.technet.com/clinth/