The first thing I noticed upon upgrading to 15.04 wasn't positive.
In fact the thing that caught my eye was that many of my icons (particularly Spotify and Banshee) in my normally beautifully clear Unity sidebar looked slightly off - that is a little pixelated and a bit rough.
After a little browse online, I discovered that I wasn't the only person to have had this problem and that thankfully this problem was patched in a Unity update.
via the synaptic package manager.