Whenever I download a .blend from someone all of the windows and settings are the way they have left them as it is saved in the file. It takes way to long to rearrange every window and toolbar to the way it is by default. Is there any tool or shortcut that can reset the UI to blenders default and just leave the actual contents of the file? The only way I could do this is by creating a new file and using link/append but this is not the best option.
When you open the file there is an option to load the UI from the file which is about to be opened. By default this is enabled, deselecting this option will keep the current settings. See image below.
Edit - Updated with comment by @Samble
In the user preferences under File there is an option for Load UI - this is the default that is used each time you open a file. If it helps you can turn it off and manually turn it on only when you want to load the UI from a file.
Once the file has been loaded it will use the setting pulled from .blend file and to my knowledge there is no "Reset to Factory UI" or "Reset to Start-Up UI" option like you can do for the start-up .blend.
Should probably be put in as a feature request as I a lot of people share files and doing it by accident is annoying as you lose your current UI and then have to either reload factory setting or your own blend file to get back your UI before re-open the file you want to load.