Bitcoin is one of those things that I know exists, but I have no real concept of how it works. Computers do maths, I think the computer that solves a thing somehow then has money, and this money-that-never-existed-but-now-does fluctuates wildly in price from day to day and people who sold theirs a few years ago would probably now be filthy rich if they still had it. Or something.
It's complicated, volatile, and a bit scary to me, and Valve seems to agree — it has just stopped taking bitcoin as a payment option for games on Steam according to a blog post:
In the past few months we've seen an increase in the volatility in the value of Bitcoin and a significant increase in the fees to process transactions on the Bitcoin network. For example, transaction fees that are charged to the customer by the Bitcoin network have skyrocketed this year, topping out at close to $20 a transaction last week (compared to roughly $0.20 when we initially enabled Bitcoin). These fees result in unreasonably high costs for purchasing games when paying with Bitcoin. The high transaction fees cause even greater problems when the value of Bitcoin itself drops dramatically.
Basically, you get charged $20 (around £15) for a Bitcoin transaction, and if mid way through a bitcoin purchase the value of the currency drops, you then have to do a second transaction for the difference in value, which will incur a second £15 fee, and it all just gets a bit expensive and convoluted to do.
I get the value of a currency decentralised from any specific nation and stuff, but I also am not going to blame Valve for not wanting to ride the wildly swinging roller coaster that is this somewhat unstable cyrptocurrency. At least a centralised government-issued currency remains fairly stable in value most of the time.