it will be very hard to invest a significant fortune in bitcoins without the government knowing it.
but it is amazingly easy to invest an insignificant fortune in bitcoins, and subsequently spend a significant one.
So true. This is what fuels the bubbles. People throw a little in for "fun" then when the price rises as quickly as it does (or can) they are shocked at how much their "little fortune" has grown. Of course governments will what their piece of it but if governments make some money off the investments they will be happy to let people use it.