I've installed Ubuntu 15.04 on my new PC with little difficulty. The machine came with 64bit Windows 8.1 pre-installed, I partitioned the SSD and HDD drives appropriately and Ubuntu went on with no problems...
... once I'd managed to get the usb drive with the installer to boot in the correct mode.
Windows had been installed in legacy boot mode, the usb kept booting in UEFI mode. First I changed the BIOS settings so that devices booted in legacy mode only. This meant that the PC wouldn't boot from the usb at all. I eventually found an option in the BIOS to force boot from usb and everything went fine.
So far everything is working okay apart from printing from usb (network printing is fine) and Geeknote connection to Evernote. I did have problems getting the Linux Spotify client to work, but the following post gave a solution: http://www.webupd8.org/2015/04/fix-missing-libgcrypt11-causing-spotify.html
I hope the above is of some use to someone!
Update 10/5/15: Had to download the latest hp-lip to get usb printing working. All sorted now