How does one measure a "good" financial bubble versus a "bad" financial bubble?
One way of doing that is to look at individual components, like this one.

In 2021, 16 companies either have or are expected to go public with a valuation of over $1 billion despite having zero revenues. That's more than double the number in 1999, three more than in 2001, and two more than in the year 2000, during the height of the dot-com bubble.

The rise in public companies with zero revenues of late is an illustration of a boom in special purpose acquisition companies, or SPACs.

Over 90% of zero revenue companies that plan to go public with over a $1 billion valuation in 2021 thus far intend on using a SPAC to do so.

A SPAC is a "blank check firm" that exists solely to list on a public stock exchange, raise money, and then find a merger partner to take public.

In 2019, 59 SPACs went public. In 2020, 250 SPACs went public. In just January and February of 2021, 170 SPACs went public.
A-Rod and Colin Kapernick have taken part in SPACs in 2021, to name just a few celebs.

“I mean, Shaq has a SPAC. What could go wrong?”
- one economist

Remember that some of these stock offerings are for companies that have ZERO revenue.
We aren't talking about zero profits, like Tesla, but zero revenue.
It enough to make one question the claim that unregulated capitalism is efficient.

Then there's the fact that people can't buy stocks fast enough.

Last week, they poured $36 billion into funds focused on U.S. equities, the biggest inflow in more than two decades, according to data compiled by EPFR, a unit of Informa Financial Intelligence.

Hedge funds are trimming bearish bets while raising their bullish wagers. Their net leverage, a measure of industry risk appetite that takes into account long versus short positions, climbed to a record this month, according to data compiled by Goldman Sachs Group Inc.’s prime brokerage unit.
The cost of missing out is looming large on investors’ minds with equities having added a stunning $12 trillion to values since March. Valuations rivaling the dot-com era proved no hurdle to risk appetite...

“This isn’t a ‘normal’ market, but as long as it continues to press higher and higher, I think we’re almost forced to own stocks.”

Bears are almost nowhere to be found, with short sales dwindling to fresh lows amid January’s retail-driven short squeeze. In fact, according to a survey by the National Association of Active Investment Managers, the most-bearish group that typically has a net-short position was 80% long in stocks earlier this month before turning neutral.

There once was a time when the smart money bet against the crowd. That time appears to have passed. Now the market is ruled by fear, fear of missing out.

The bubble goes far beyond just stocks. Bitcoin at $50,000 is a good example.

And then there's the historic, unprecedented bubble in bonds, as reflected in global negative interest rates.

Germany’s biggest lenders, Deutsche Bank AG and Commerzbank AG , have told new customers since last year to pay a 0.5% annual rate to keep large sums of money with them. The banks say they can no longer absorb the negative interest rates the European Central Bank charges them. The more customer deposits banks have, the more they have to park with the central bank.

That is creating an unusual incentive, where banks that usually want deposits as an inexpensive form of financing, are essentially telling customers to go away. Banks are even providing new online tools to help customers take their deposits elsewhere.