Low-resolution icons displayed in Dock and Launchpad
Cheekily adding this as an answer based on a comment above as the commenter didn't include it.

The cause appears to be a mystery, but if you remove the icon from the dock (just drag it away until you get the vanishing smoke animation), and re add the icon (run the app, right click on the dock icon and click Keep, or drag the icon back in from the finder) to get the full resolution icon for any app that is doing this.  It's a workaround that doesn't explain the issue, but should be good enough.