Shamus: I bought a 50mm about a month ago but haven't had the time to "play" yet. Soon. BTW did you see how much a 1.2 costs vs the 1.4?...WOW Too much!
Hint: I have a 100-400 IS which has been my mainstay since I started shooting. It's great for birds in flight too, heavy but not terribly so. I'd like to move to the next level with something that gives me a little more reach. Hence the 500 vs 600 question. I can buy a 500 for about $1000 less than a 600. Some folks seem to lean in that direction because of the weight of the 600, about 3 lbs more than the 500. I don't really see that as an issue because I likely will never lug either beast without my "carriage". Though the savings might launch me into that full frame dslr I want.