I have a dell precision M6300, Vista Ultimate 64-bit, and I have problems with dropping connections with a Wireless-N router using an Intel(R) Wireless WiFi Link 4965AGN adaptor. The radio quality is always marked as excellent, but the performance degrades rapidly after a couple of minutes of use until a level that it's almost unusable.
I have an identical PC (identical hardware and OS, same version of drivers for the 4965AGN adaptor. That laptop has no problems at all.
When I run the laptop in safe mode, it hasn't any problems either, so it must be a software problem. I have downloaded and installed the latest version of the drivers.