Quality of life updates are usually small changes that make navigating the game a little more convenient for everyone -- like highlighting numbers in green when it's an upgrade in the Quick Comparison window, for example, or marking the mini-map with a star icon whenever a Legendary item drops.
If you're having trouble narrowing down exactly what kind of changes qualify as "quality of life," here are a few more examples of things already in Diablo III to help get the creative process rolling:
- Artisans can now craft items with materials in your stash
- You can disable the confirmation box when salvaging Rare items
- Combat notifications for party members