Sometimes when I first boot in to my Windows 7 (Home Premium SP1), I get a red "X" over the Wifi indicator in the status bar.
Hovering over the indicator shows the popup "Not connected. No connections are available."
If I then disable the "Wireless network connection" (Intel Centrino Advanced-N 6230) and re-enable it always connects immediately and all is well.
This seems to rule out hardware or driver issues. Any thoughts?