I still use MP3, for compatibility reasons. I have a lot of music from ages ago in MP3, I have no idea where some of it came from so that's not going to change. The rest of my music is all encoded in FLAC on my NAS box - but FLAC is way too big for an SD card, so I copy all of that to MP3 in a "lo-fi" folder.
Even today, MP3 is the only format you can rely on being able to play on an arbitrary device (certain early Sony players excepted). I'll only get proper equipment that plays FLAC, OGG, etc - but you've always got those friends who insist on using some weird device and then moans that it's not compatible with your standards-compliant kit.
(Yes, I'm looking at you, Apple.)