Pentax DA 50mm 1.8 - anyone using it yet?

I'm looking at fast primes to use for concerts when the light gets too poor for my f2.8 zooms (like it did at the last gig ). I'm looking at the 50mm options but there doesn't seem to be much user info out there on the latest DA 50mm 1.8 lens. I don't mind the plastic build (I've got the 35mm 2.4 and like it), my priority is more to do with performance wide open.

Anyone using it yet? How's it perform wide open? Comparisons to the SDM 55 1.4?