I am now 3000+ ly from civiized space and it's almost to the point where I get annoyed when I see completely undiscovered systems, cause I have ly's to cover and scanning a 30+ planet system usually takes an hour...
I'm now not even bothering unless it's got something interesting, I'm even passing on heavy metal planets..
update:
I started seeing undiscovered about as fast as I passed the coalsack nebula (I'm sure I left a few there) and that's not even 500ly out.