Lots of personal preference on organizational structure, feature differences (can't share tags yet), and sometimes client capability (ie: might use folders if tags aren't easily exposed in the device.)
For instance you might make a 'Followup' tag rather than moving todo items into a single folder, because you want everything still sorted in folders by category first.
Same goes for a Tidbits tag that could span items anywhere.
Or broad to narrow categories rather than under:folder searches:
T-Support
F-Team
F-Tickets
Or the reverse:
F-Bugzilla
T-RFE
T-Bugs
Use tagging alert you about particular addressees (bosses) that are members of the convo, or specific content words of a message using filters > tag with. (There's also a slick
Colored Emails Zimlet to accomplish the same thing, but that can only be used in the advanced AJAX client.)
For the future we plan sharing, more colors, as well as hierarchy trees for the tags.