Actually, according to MS, BootVis does nothing in the way of optimizing boot time.
http://www.microsoft.com/whdc/system...t/BootVis.mspx
"Please note that Bootvis.exe is not a tool that will improve boot/resume performance for end users. Contrary to some published reports, Bootvis.exe cannot reduce or alter a system's boot or resume performance. The boot optimization routines invoked by Bootvis.exe are built into Windows XP. These routines run automatically at pre-determined times as part of the normal operation of the operating system."
It can tell you what programs/drivers are taking the longest to load though, which can be useful in helping you to decide which should be axed from your startup routine.