shutdown time depends on a lot of things ...
cpu usage ... np. of programs runnin ... etc
also it keeps increasing as u use ur system ...
also dependent on disk fragmentation
also windows waits a certain time to allow apps and services to shutdown automatically
use THIS tweak to lessen it .. (win xp)
there is also something like waiting to flush the virtual memory or somethign
i forgot the reg tweak but there are software available to do this ..
check the following links .. it'll help u shut windows down faster
however i must warn u ... it is not recommended to use these software as it disables flushin of virtual memory .. which isnt recommended either
but it does its job well
*www.webmasterfree.com/2004/0528.html <=== a utility called super fast shutdown ... try it out
*www.nonags.com/nonags/shutd.html <=== some more useful software with description