By sheer chance, I just found out how to search for tracker tags in nautilus (those are most easily added with 'tracker-tag -a').
Stop beagle if it is running.
Start 'nautilus --browser'.
Ctrl-F, and type tag
I really simply tried a bunch of things out of frustration this morning and this one worked.
This search can be added to Nautilus Side Pane as a bookmark. Click on the button on the left of search bar This will switch from search to "Go To location". Click on the button again. This will turn the search bar into a solid box that will say 'Search for "tag
ourTag"'. Now this can be dragged to the Side Pane.
Yesterday, found a similar way of doing this in KDE 4.4. This requires nepomuk to be enabled. File tags can be added in dolphin. Then one can add a "Folder View" widget to the desktop. In its preferences, click on Location and enter
"nepomuksearch:/hasTag=YourTag1 OR hasTag=YourTag2"
(-hasTag to exclude is supposed to work too)
The plasma widget will now show files that match the tags. Judging by google search, "=" in this command used to be ":" in earlier versions of KDE. The command can also be entered from dolphin (search bar) and konqueror.
These things are nice but also apparently well hidden!