Yeah, I just got the NX100 myself (and it shares its sensor with the K7, not the K20, as seen
here), and it's a hugely enjoyable camera... With the 30/2, it makes really stunning pictures (damn, this lens is
sharp!).
They really nailed the manual focus feel of their lenses, BTW. I'm used to manual focus (got the samyang 85/1.4, a lot of Taks, some PK and PK-m, and so on...), and using their fly-by-wire focus ring just feel like the real thing : properly damped, really smooth and responsive, a pleasure...
And coming back to the OP : for me, size, IQ
and price are the main appeals of mirrorless. This NX100+20-50+30/2 combo was the same price as a brand new FA35/2, so it fit the bill quite nicely for a small, purse-sized, normal FL, portrait-oriented purchase that no DSLR lens could satisfy...
And I've found out that for those family events, it's a way better form factor than my big black K5 ever was! Yeah, following running kids is a real pain and near impossible, but apart from that, those mirrorless are more than capable
today, so I guess tomorrow they will be quite good alternative to DSLRs.