Buying and selling online can be divisive, with some people unwilling to part with real money and some countries even disallowing services such as PayPal. Bitcoins are a unique currency, existing purely online, and WordPress intends to honor their use. As part of their mission to "make publishing democratic", as Andy Skelton puts it, Bitcoins are now to be accepted.
Paying for upgrades on WordPress is a real thing and for some of the site's premier bloggers it can make sense. More than 60 countries don't work with PayPal - Argentina, for example, isn't fond of American dollars, meaning there are some potential customers going amiss.
Bitcoin is how WordPress wants to help bloggers from all over the world get themselves further into the digital world of self-publishing. It isn't an entirely flawless method of payment, for refunds aren't possible using Bitcoins, but WordPress says that they will still honor any refund requests, returning cash in Bitcoins.
Spending Bitcoins isn't a problem, but getting them is more difficult. Therefore, they have explained how to get your hands on the virtual currency by linking to We Use Coins. Coincidentally, The Verge's Adrianne Jeffries published a piece today about certain points of Bitcoin as a currency, which may be of interest.
Source: WordPress official blog