In pirate circles it is the defacto lossy standard. Using LAME to encode it to both v0 VBR and 320 CBR is basically every scene and P2P release. All the big music sites like WCD (now gone), RED, APL, NWCD, Petros etc all release in MP3 for everything.
AAC and OGG have not caught on with pirates because they're not as ubiquitously supported when it comes to device playback. Personally I was getting MP3 320's but I've switched to FLAC now since it's lossless. I can then transcode it in to whatever format I need (ALAC, AAC, MP3 etc) for the specific playback device I'm using.