There are some significant updates including drivers for WiFi and other modules, and bug fixes for Ethernet and Button.
This release requires reflashing the mainboard. The tool at Start->GHI Electronics->GHI NETMF v4.1 SDK->Firmware Update->Fez Spider Updater makes this easier than otherwise.
It requires going into serial mode to reflash the bootloader, which means flipping little switches on the mainboard. Be aware that the updater does not update the MAC address so you have to update that manually if you want to use Ethernet, using the MFDeploy tool (Start->Microsoft .NET Micro Framework v4.1->Tools->MFDeploy.exe) then choose USB then choose Target->Configuration->Network then change the field MAC Address to the text written on the mainboard sticker but with dashes between each pair of characters (e.g. if your mac is 123456789012 then you should use 12-34-56-78-90-12 in the MAC Address box).
I will try to post more on this later.