CVS may have had serious flaws, but I find Linus' original revision control practices to be less than optimal:
"The Linux kernel source code used to be maintained without the help of an automated source code management system, mostly because of Linus Torvalds' dislike of centralized SCM systems.
In 2002, Linux kernel development switched to BitKeeper, a SCM system which satisfied Linus Torvalds' technical requirements."
Nearly a decade without a revision control system?