I was thinking about buying a TB and then cutting it down to fit in a microcache--a "micro bug" if you will. However, a tagless TB would be better as I think we all are on a tight budget. I can create a small metal tag that can be used. The problem, like another poster said, would be for most people creating a durable, official-looking tag.
If running out of numbers are a concern, a 6 digit alpha-numeric (A-Z and 3,4,6,7,8,9 - the rest are deleted to reduce errors, i.e. 2 and Z look similar unless very clearly written out) yields a billion numbers, while 8 digits yields about a trillion.
Also, I would be more inclined to buy a TB number at maybe a $1 a piece, especially if I get the number instantly.
If the TBs were free it would be a huge problem as there would be the tons of TBs floating around. People could make all of their items TBs and we'd be deluged with them.
But overall, I think a tagless TB, or DIY TBs are a good idea.
CR