I used to use Bootvis to optimize without a problem. After several recent Windows critical updates, Bootvis didn't work anymore: "Timeout Error! Bootvis is unable to complete the defrag". My bootup time from pressing power button to all taskbar icons loaded went from 38s to 51s (with NAV and NIS icons taking a long time and loading last instead of first). I tried to do a System Restore to an earlier date but couldn't so I ended up doing a Upgrade Reinstall/Repair.
What I found out after reading the "Fast System Startup for PCs running Windows.doc": the OPTIMIZE function of Bootvis is actually a normal Win XP function during IDLE periods. Now I just use Bootvis to measure startup times/processes. To OPTIMZE: I simply let the system idle with screensaver for 10-15min. Currently my startup time is back to ~37s.