Right now: I use it as a Flashrom rig, for flashing BIOS chips.
The new Raspberry Pi looks powerful enough to use as a media center PC, I ordered one and want to see if it can do that well enough (read as: I’m curious to see emulation performance.)
I've been happy for a year or two (not even sure, now that I think about it...) with two Pi3s running openElec. Both run over wired ethernet to SMB media server. I'm generally stingy with my storage, so I usually opt for the 1080p file sizes. I don't know how well or if it can handle 4K.