The upgrade from 8 to 8.1 worked great for me. In addition, if I choose to set the Windows bootloader as the first (default) option, every time I boot or restart the computer there is now a new blue screen that looks like the screen you see with the "Advanced Startup" screen that first appeared in Windows with Windows 8. From this screen, there was an option to continue booting to Windows 8.1, Boot to Linux Mint 15, or boot with EFI USB. Surprisingly enough, when I selected the Linux option, I was greeted by the GRUB menu. Since I'm seeing this blue screen any time I boot or reboot to Windows, I just made the Windows bootloader the default option. That's a whole lot easier than it was before with Windows 8 and all the frustrations with the BCD, boot-repair, rEFInd, etc. Trivial bonus: you can use the mouse/cursor on that blue startup screen as well.
Here's a quick picture I snapped of the sceen: