Skype calls or Steam are/is silencing my games/music/whatever

This isn't actually Skype's fault - it's Window's. The default setting in Windows is that a call will lower the volume of other applications by 80%! Thankfully, this is a quick fix. To solve this do the following

1. Right click on the volume icon (the little speaker in your notification tray)
2. Select "Sounds"
3. Choose the "Communications" tab
4. Pick whatever option you'd like.

For more details see here.