Make it really obvious where newly-installed apps can be found

Ideas:

1. Highlight the applications icon in kickoff / the category in kicker.
2. Add a recently installed applications section to the history tab for kickoff, and recently installed category to kicker. Clicking on it would bring the user to the applications tab in the proper category and highlight the application.
3. Add a badge to the applications tab and the different categories that have recently installed applications.
4. Add a button in Discover to show the application inside kickoff/kicker (don't know if this can actually be done tho).

Use a prettier background for the lock & login screens

I would vote for option 4, but with a darkening effect (or even a blur). Option 2 would be great too. I would avoid single colors because strong colors would look out of place with Breeze, and breeze-like colors would look kind of bland as a background.

Don't use transparency when moving windows

+1. This always looked weird to me and it's one of the first things I change. There's no practical reason for this.

Make it really obvious where newly-installed apps can be found

There are a few ways that this can be done. We also have a few menu ideas out there, so this would have to fit all instances of the menus we have. I like the way that mobile does it, they install an app, they add a dot next to the app that tells you it is new. Windows also highlights the menu item until you click on it. I would also want to use something a little more gimmicky, such as dropping an icon into a desktop area that can clue the user into looking this up. Or even open the install folder or menu automatically after being done installing.

Use a prettier background for the lock & login screens

We had a discussion on this some time ago. The only technical problem appears to be that the images displayed are not dynamic, so they could "not" be your desired wallpaper, for example. Instead, the user would have to change this on their own. I am all for using images, maybe the default wallpaper. But let it be known that this question was a bit polarizing since many didn't also agree on what image should go there as a background. Whatever image it is also, it won't be able to be replicated in GRUB since that doesn't work there.

Use themed icons from apps' desktop files anywhere KWin displays icons

I think this "should" be consistent and use the same icon. Or the icon that goes along with the theme.

Show Desktop widget should be present by default in new installs

This could work, except we already have a menu, more of them would be hard. I would be in favor of a key combination to show the desktop, a button on the taskbar, or a hot corner enabled by default?

Redesign Breeze theme icon for Virtualbox

Yeah! We could create our own.

I found someone to make us a new Virtualbox icon! D10212: New virtualbox icon