Agree, I think crossing the $1B (or $100 per coin) mark is when a change of perception occurs from "experiment/toy/crapshoot" to "viable speculation" for bigger and more conservative money. To use terminology from stocks, Bitcoin right now is a microcap (between$50M and $300M) , and can't even be considered "small cap" until its market cap is between $300M and $2B. Midcap would be between $2B and $10B, and large cap above that. If you assume all 21M coins have been minted, Bitcoin's market cap would finally be considered mature and liquid for the biggest and most conservative money managers if it's also trading at $500 or above.