I usually say something along the lines of "yeah, I am trying to get back into shape and run competitively". Then the question about how many miles per day I run, and I have got it down to "I run about 50 miles on 6 days of running per week, so about 8 miles per day". At this point in the conversation, it seems that people A) are impressed B) Don't believe me C) think that I am strange and that running must take up 90% of my free time. If I go for a run during lunch and cover 7 miles in 50 minutes, people are surprised that I got in 7 miles and I'm not lying down and puking after the run. They also can't understand that I really just got out on the road and ran 7 miles in the time it took them to check their fantasy football team and check facebook.
The question always comes about a marathon. I haven't ran one yet, and this seems to be more of a qualification to be a good runner (outside the running community) than running 5 minute pace for a 5k. Another common event I get asked about is the mile. My mile PR isn't great, but people seem to think that a 4:25 is close enough to 4 minutes and they know that 4 minutes is really fast.