I've done this one before but I gotta do it again. :-)
In more and more applications that use tree-controls for selecting folders, I've been seeing Select Folder dialogs containing editable text fields into which you can paste a path that's been copied to the clipboard. Getting a path into the clipboard is easy in Win XP with any of several free shell extensions that can be downloaded from the web, and it's built into Win 7 and Server (and possibly also Vista, for all I know). And it's a complete breeze to do at the command line in either cmd.exe or 4NT/Take Command console windows.
Pasting a path from the clipboard, rather than having to click/click/click/click through a tree-control, can save a whole lot of time (and in a long day when the mouse has been used constantly, every feature that reduces unnecessary mouse moves and clicks sure helps cut down on "mouse fatigue").
Another dialog enhancement I'd love to see has to do with Snapshots -- a "Manage..." menu item giving you a dialog for deleting or renaming individual Snapshots. I know this can be done by holding down Shift as you click a specific Snapshot item. But it's not an easily "discoverable" feature. Or, if you prefer to retain the shift-key approach, how about having a "Manage..." selection that appears (instead of "Save...") when the shift key is pressed and the Snapshot icon is selected?