I'm not sure if this has been covered sufficiently already, but I've heard lamentations by various writers about the lack of a keyboard shortcut to bring up the file-tagging popup in the Finder. While none is provided by default, one can easily be set up.
In previous versions of OS X, the File menu had Label: followed by the row of colored cells. In Mavericks, the row of tags is still there, but the un-selectable Label: has changed to the selectable Tags…, which opens the tagging popup menu next to the selected file.
This process may already be familiar to MacOSXHints readers. Go to System Preferences » Keyboard » Shortcuts » App Shortcuts and click on the + button.
In the window that appears, set the Application to be the Finder, and enter Tags… in for the Menu Title. (To type the ellipsis character, use Option+semicolon, rather than three periods.) And then, of course, set your preferred shortcut. I like using Cmd+Opt+T.
[crarko adds: Handy. I hope this kind of customizing does not disappear in Mavericks' successor. I fear the worst.]
Mac OS X Hints