You can add me to the list of people who like the Fly. I haven't used it in the wet, but my early impressions are very positive.
Steve Bullman, your impression of its size was right on. According to my trusty vernier caliper it measures a full 12 mm (unladen). By comparison my Sportline was an honest 11 mm, and my Yale XTC was 13.5 mm.
Not that I'm complaining; I find the extra mm. makes the Fly more comfortable in hand than the Sportline, yet it is still a lighter and more compact line than regular 1/2" arborist ropes.
And, in addition to all its functional virtues, it is an attractive rope. And that's good! Why should only the rock jocks have pretty gear?