Win7 libraries have a default folder location, but there are times I want to save to a different one (eg My Documents vs Shared Documents) but I can't find any way to specify any of the other locations from the file-save dialog.
Under the list of libraries in the dialog's left side pane, expand your library. The folders that are included in your library will be shown. Click on the folder that you wish to save to. The file will now be saved in that location.
Edit: The blue arrow shows where to click
Edit: In the case of the old save/open dialogs, you go into your library, right click on the folder that you want to save in, and select "Open Folder Location".