When can I actually use Bitcoin as a currency rather than a speculative investment asset? That's when I want to buy Bitcoin.
What is "currency" for you? People refer to "currency" all the time as if it was one thing. Cash is one kind of currency, plastic is another, bank account - yet another, savings - yet another. Converting between those is not instant and not free. Bitcoin works OK as a bank account. That is "currency".
Though Bitcoin is NOT yet a currency. It cannot store value, the volatility ensures that.
An example to illustrate: Part I: Cash - Bank etc. If I have $2000 in Cash, Credit Card has a balance of $1000 (maxed out) and $0 in my Checking/Chequing/Savings account (bank).
I can visit a branch that's 10 mins away, and deposit the all the money, total wait time would be I can immediately go to an ATM and withdraw $500. (transaction cost free - $0.30)
After that I can walk back to my home and access all the $1500, this can be:
a) $500 transferred from account to high yield savings account. (transaction cost free)
b) $500 transferred to grand parents using interac (transaction cost free - $1.00)
c) $500 transferred to credit card (transaction cost free) - Note: (i) Credit cards can take up to 3 days to reflect the payment (ii) Credit Cards will consider the original transaction date as the payment date thus not incurring interest for the delay in reflecting the payment and (iii) some credit card issuers will let you make a transaction before the payment is reflected thus reducing the unfortunate "Check kiting"[1] nature of the delay in reflecting the transaction.
Part II: Cash - Bitcoin - Cash Will not go into explaining this in detail, but just answer this 1) Can you take cash and transfer it to bitcoin without using the bank? 2) Will it be nearly as quick converting between instruments as traditional stores of value? 3) In a day or two when you want to make a purchase can you guarantee or even confidently assume that the value will be the same as when you deposited it? Hell can you assure yourself that the value will be the same [1] http://en.wikipedia.org/wiki/Check_kiting