I recently purchased a Lenovo Ideapad Yoga 11S, preinstalled with Windows 8. Wifi worked fine. Subsequently I upgraded to 8.1. Ever since, my Wifi connection is unreliable. It disconnects itself after about 30 minutes. The easiest way to reconnect is to switch off Wifi and then switch it back on again. I have Connect Automatically as the default but it doesn't. I have to tell it to connect. Investigating further, it appears that the Wireless Network Adapter is disabling itself. My home wireless LAN comes from a Century Link PK5001Z Modem/Router.
Obviously this problem is not a showstopper as the fix is fast ans simple, but it is irritating.