A friend of mine, some might know him from VC or Boards.ie (HectorJelly) played a stupid amount of these over the course of a few months and his stats were quite amazing, now he is quite some player and if he had those swings the average players would be crazy. Like byron said 500 run loss is not unlikely!
So if you were to play say 1 or 2 sng's 5 times a week, say 30 in a month you could go 2 years losing but still be a winning player at that level!
Oddly i have just finished reading his blog, haven't looked at in a long long time but i have always enjoyed it.
I have also played many, many sng's with him in the past and agree he knows his stuff, small world huh?