How are you measuring the size of the "actual" economy?
Take a look at the Wiki list of companies taking Bitcoin and sum their total estimated turnover. Obviously this is highly imprecise since there is not a lot of information available, most if not all are privately owned etc. but I would not estimate more than a couple of million USD a year. Even that is highly optimistic because most are likely only taking a fraction in BTC right now (e.g. I would wager memorydealers currently loses money on promoting Bitcoin). The list doesn't contain any seriously large company, or even medium sized company that I can see. Tradehill proxying Amazon may be the largest, though I doubt they have had more than a few hundred customers for this so far.
If you take a highly optimistic 5 million USD, then at 7 million BTC the exchange rate should be around 0.7 USD/BTC now, not $15. Since it seems obvious there is a lot of work to be done before Bitcoin can even be technically conscionably accepted
by less than adventurous retailers (like Amazon), it will take that much time for the economy to grow by those numbers. Until then, the speculative ratio is over 20:1. If it goes to $30 again, that's over 40:1. $60? 80:1. How much is not ludicrous?
I think the two important indicators are network difficulty and exchange volume / price, both of which have been growing like wildfire.
Neither of which reflect the actual economy size. As long as it's worth it, new miners will join, but they are speculating just as much as traders.
"Someone" cashed out over a million bucks today
Are you looking at blockexplorer and a known exchange wallet address? Otherwise it could be anything but a cashout. It could be the exchange moving funds between wallets for all we know. If you're looking at the exchange turnover, how do you know it's not just a few traders trading the same balances back and forth? None of this has any correlation with the actual economy, which consists of people paying eachother for goods and services. Couple of years ago everyone thought mortgage derivatives consisted of real value too.
network difficulty is a reliable measure of the size of the economy.
Obviously I completely disagree with this. By this argument the economy has grown incredibly fast over the last couple of weeks and will suddenly stop growing much between the next 2 increases (according to chodpaba's numbers).
If you know how to reliably measure the "real world value" of assets, maybe you should tell Wall Street.
Hah, Wall Street is not interested in real numbers, you should know that by now. Some bank got sued by its own shareholders because they paid out almost double the bonuses (4+ billion USD) than they actually made (2-ish billion USD).
Speculative expectation has been setting the price of things like houses, oil, bread, gold, and stocks ever since civilization moved to from a barter economy to a monetary economy. Why should the price of bitcoin be any different?
Hopefully because the underlying system is more robust. As the real economy around it grows, bubble type activity should subside, but it does need to survive that first. If it fails on that count, Bitcoin will be remembered as a classic ponzi scheme, albeit a brilliant one.
