These are approximate currency emissions for various established world currencies - from large to small:

 Euro (EUR) 1035 billion USD
 US Dollar (USD) 850 billion USD
 Chinese Renmibi (CNY) 492 billion USD
 Swiss Franc (CHF) 50 billion USD
 Australian Dollar (AUD) 32 billion USD
 Costa Rican Colon (CRC) 1.7 billion USD
 Eastern Caribbean Dollar (XCD) 1.1 billion USD

Sources: major currencies, CRC, XCD.

The total number of Bitcoins mined so far, and potentially available for use (not accounting for people who lost their keys), is nearly 11,000,000. At $140 per Bitcoin, the current value of Bitcoin emissions is $1.5 billion.

This is larger than the Eastern Caribbean Dollar (used by some 600,000 people, as well as partially in off-shore banking). It is almost as much as the Costa Rican Colon (national currency for some 4 million people).

Does Bitcoin even have 4 million people who have access to it? Does it have 600,000 people who use it on a daily basis? It seems doubtful.

According to the 2010 Federal Reserve Payments Study, in 2009 there were 115 billion of just non-cash transactions in the US:

 Checks 24.5 billion
 ACH 19.1 billion
 Credit card 21.6 billion
 Debit card 37.9 billion
 Prepaid 6.0 billion
 ATM 6.0 billion
 Total 115.1 billion

In the US in 2009, that averages out to about 1 non-cash transaction, per person, per day. I have no estimate for the number of cash transactions in addition.

Meanwhile, the average number of Bitcoin transactions per block right now is 335. That's on the order of 50,000 transactions per day. Drawing a parallel to USD, that's, perhaps... equivalent to 40,000 people regularly using Bitcoin? But with many of those transactions being speculative, due to recent publicity it has received?

Bitcoin has promise, but it has major shortcomings that have not yet been overcome.

If it becomes more successful, those who benefit from the current financial system may act to make exchanges into and out of Bitcoin a lot more difficult - it may become a currency only exchangeable in black markets.

It does not seem to me that a price of $140 reflects real, long-term demand for Bitcoin that's sustainable given the options that exist right now. If you're buying it at $140, you're making a bet that it will be more successful in the future, and it won't run into major obstacles.

That may turn out to be the case, but the more the price goes up, the more it's jumping to a conclusion before it has happened. In other words, a gamble.