Labels are all very well, and I suppose you can always replicate a file to some folder marked “Urgent” or “Action.” But there ought to be some way to “flag” a file as a priority with one click, as for example in Apple Mail.
And/or some way to “pin” frequently used files or urls, a la the Bookmark Bar in Safari or Firefox. The long empty status bar underneath the toolbar would work well for this – ideally you’d just drag the file onto it.
The toolbar itself would be a good place for this as well. It’s almost empty in my case, only shown for the search field. So there is lot of space for important files/groups there.
A second on the flag suggestion…this goes along with my suggestion in another thread for an alarm/calendaring function. Since DT is now so useful for everyday PIM, there is a great need for more functions like these that are standard for PIM’s.
FWIW, I use the Label functionality for this purpose. Adding a label changes the document icon to the desired color, and the label can be used as the basis for a smart group. In fact, for my purposes, a label is better than a flag. With more than one label color (as opposed to a binary flag/no-flag), I can “flag” documents for a variety of different purposes.