I've heard that NTFS compression can reduce performance due to extra CPU usage, but I've read reports that it may actually increase performance because of reduced disk reads. How exactly does NTFS compression affect system performance?

Notes:

• I'm running a laptop with a 5400 RPM hard drive, and many of the things I do on it are I/O bound.
• The processor is a AMD Phenom II with four cores running at 2.0 GHz.
• The system is defragmented regularly using UltraDefrag.
• The workload is mixed read-write, with reads occurring somewhat more often than writes.
• The files to be compressed include personal documents and selected programs, including several (less demanding) games and Visual Studio (which tends to be I/O bound more often than not).