The miners mine and hold, other mine and sell.

Investors and speculators buy, hold and sell.

You can buy random items in auctions and through the forums.

What are the reasons for the bulk of the bitcoin transfers? I read an article underlying the "dark side" of the internet and TOR network, and they seem to point out that bitcoins are now nearly the exclusive currency for the online "black market" (Note, they are not saying bitcoins are exclusively used for black market transactions)

What have you used bitcoins for?

Miner
Investor
Black Market
Other - explain