Launcher runs fine, but upon starting the actual app, 13w38a and later hang at the MOJANG logo screen. CPU pegs at 100% utilization, but game never progresses past this screen.
13w37b and earlier work fine; this started with 13w38a and exists in 13w38c.
I can confirm. Does not work on 13w39a, have not tried on 13w39b but so far its not working still.