When you save a file into a Windows 7 library through the common "Save As" dialog, it ends up in just one of the folders that make up that library. Here's how to customise the default save location for any library.
As an example, if you were to save a Word document in your Documents library using the Save As dialog, it would end up in your My Documents folder by default. But what if you would prefer that the files get saved in a different folder that's still part of your Documents library? Like one of your Dropbox folders, for instance?
Changing Default Save Location: Method 1
You can simply click the "Includes 3 locations" in the Open/Save dialog to make your way into the quick properties window.
From here, you can easily add or remove library locations, and if you right-click on one of them, you can choose "Set as default save location". Useful!
Changing Default Save Location: Method 2
You can also head in Windows Explorer down to the Libraries section, right-click on any of the libraries, and choose Properties.
This will take you into the extended library properties window, where you can add or remove locations, and click the Set save location to set the default.
You'll note in the screenshots above that I've included my Dropbox documents folder—this is a really great way to include your Dropbox folders in the default libraries, and set the default location as your Dropbox instead of the regular folders.
Note: While we used the Documents library as the example here, this should work for any of your Windows 7 libraries.