With the recent change in the Dropbox for Mac architecture, when you search for files over a certain size in the Finder, all of your Dropbox files show up with the total files size listed, even if they are online-only (so actually close to 0 kB stored locally on your hard drive). (The previous version showed these files as 0 kB, which had its own problems, as you couldn't search by file size).
For those of us who prefer to manage the online / offline decision manually, it would be fantastic to be able to search using a (online-only vs. available offline) flag, so that we can find large files that are currently stored locally and then choose to make them online-only if we aren't actively working with them.
This search could either be facilitated by making a searchable (online-only vs. available offline) flag that could be added to a Finder search (which is probably harder because it involved integration with Apple) or just to be able to do it from the local Dropbox app or via the Dropbox web interface.
An example search would be [ file size > 100 MB ] & [ available offline ] -> results, sorted by file size, larger to smaller. With the results in hand, you would be able to select the files you want to make online-only.