Consider_this

No Gold Bubble

Your theory (taxi driver, hyperbolic curve) is not a necessary component to a bubble -- only that the bubbles have been allowed to grow and involve people on the streets. There are plenty of bubbles that have burst much earlier before growing to "down to mainstreet taxi driver" status.

You want to test for bubble in gold? Go to SA archives and look at any articles that bash gold. Look at the comments. Then go to any articles that praise gold, look at the comments. Put the "agree" and "disagree" comments appropriately and you'll get your indicator.

My non-scientific observation shows a HUGE number of people following gold -- that is your indicator. You want it to grow and grow by a significant percentage, and if it stagnates and shrinks, your gold investment is in trouble. A leaky bucket in following is a bad scenario to try to grow gold demand.

The number of people who go fanatic about gold is increasing; and their conviction is downright scary in the -- "I'm so sure! It can never happen other way". The last time few times saw this psychology:

1. Oil will go to 200, it can't go below 100!!!! There's no production capacity left! Peak oil!
2. Houses only go up! They aren't making anymore land! Rent and throw money away!
3. Nothing matters except eyeballs and clicks!! pets.com has huge amounts of clicks on first day!! You can't lose! Traditional companies are so passe!
4. Fiber optics mania. The orders for fiber cables have tapped out next 30 years of production!!! Nobody can buy fiber optics fast enough! You can't lose investing in fiber!!!

I say... if you're right, good for you. I choose not to play manias. At some point, you're going to have to buy medicines, food, oil and household goods. When that time comes around, you'll need to talk to "my" companies; whether we exchange in gold or not.