G'Day Ken,
I had an OM-D E-M5 for about 8 months but lost it... long story
... but I now have an OM-D E-M1.
As an astro camera, its not in the same league as a full frame camera with nice big, deep pixels for low noise, but as a small, light general purpose camera with the occasional astro use, its great. There's lots of really good glass available in the m4/3 and 4/3 range, from Zuiko, Leica, SLR Magic, etc.
I'm happy with the occasional nightscape I've taken with it so far, but there is more noise than you'd get from a 6D or whatever.
As an original OM-1 guy myself, sticking the OM badge on it I thought was a bit ambitious, but Having had both models released so far, they both live up to the OM expectation IMHO.
Al.