I've had problems with Vista spontaneously disconnecting wireless or even turning it off completely (and it only eventually realises this after a reboot) or with it failing to notice that I've plugged in the LAN cable. It is really annoying.
What kind of machine? After software updates, the old 3945 worked reasonably well in XP and Vista, but for a full year there were loads of issues. Now intel has replaced that with the (WiFi Link) 5100 and it's a big piece of crap. I've seen it happen with me and others, the wireless just disables itself and vista thinks it's enabled.. flipping everything around has no success (enabling disables the hardware) I hope that the most recent drivers (that's august or october) give less issues.