Was it one single update, or did you get a batch of them at once?Also, we will need a LOT more information than that to even get started.Check Event Viewer. Are there any error messages stamped around your startup time in the System or Applications logs?Check Device Manager. Is anything showing up with a yellow triangle?
Also, what programs do you have that launch at startup? Any one of them could be the culprit, or you could simply have too many of them and their net effect is a slow startup.
sometimes immediately after a WU it takes a while to install before windows starts. does it continually slow after several reboots?