[Quiet Man Cometh]

Some will remain permanent, like the peacock set I believe, and some will change. Occasionally items will appear in the token shop as part of events and those may be there for a limited time frame.

Not an official answer either, but this is what I've noticed as a user. :)

You gain tokens through forum achievments and from event posting and participation. They are not tradeable but since the items in the token shop do change sometimes, it's always worth hanging on to them. You can see some of what you can do to get tokens under the "achievements" link at the top of the page by your user name. Not all are there though. Some are secret and you find them as you complete them. ;)