Just a heads up to anyone contemplating an upgrade. I would recommend not putting Ubuntu 15.04 on a server just yet, not sufficiently stable. It has a few things like occasionally DNS doesn’t come up after a boot, audio doesn’t work if connecting via x2go, sometimes locks up when you attempt to shut it down, sometimes processes get stuck. None of these things were an issue with 14.04 LTS. Just getting a basic desktop up eats a bit more memory than 14.04. Part of this is that it starts a lot of unnecessary junk. With Mate desktop, it starts Abiword when you login for reasons nobody seems to be able to explain.
A few pluses with 15.04, if you’ve got an Nvidia card, the nvidia drivers from the distribution work now. No need to grab them directly from the Nvidia site and manually install, in fact that, on 15.04, now fails. There is a build for Blackberry. No idea if it actually works since I don’t have one to flash and potentially brick to try. In general there are some new toys and more documentation than in 14.04 LTS or 14.10.