Blogger Chris123NT is reporting that the LUAFV driver, which controls UAC in Vista, can cause latency issues if the controversial feature is disabled. Apparently, once UAC is disabled, a registry tweak that disables the driver in question also needs to be applied if the user wants to have solid boot times back (improved boot times obviously vary from machine to machine). The problem occurs in both Vista RTM and the current beta build of Vista SP1 (6001.17042). This seems to me like yet another reason why it’s not a good idea to disable UAC, but I'm sure UAC haters will have a very different perspective. It will be interesting to see how fast Microsoft will patch this problem, considering how important security is nowadays.
News source: Chris123NT's Blog (Thanks hypatech & TrevPlus)