Tip for users running 16.04 (xenial) about system updates
When running 15.04 if an app appears as an update in System Config > Updates that's not a problem because, well, you update it anyway but on 16.04 if an app shows as an update but you know it's a vivid version only you can think "I don't need that, I'll wait to install it".
And here's the problem, the update system stops searching for image updates because it thinks there's one waiting in the queue already (that vivid app). So you need to install any app that's waiting there if you want system updates!
Already fallen over that one yesterday...