I think the biggest issue is having too many games on the go. this leads to mass resigning/timeouts or poor play. I ran up a silly number at one point and I needed to play far too quickly to make all the neccessary moves. I played on in all my games but not very well! i know talking to some of my opponents that they have mass resigned games. There also the last minute emergency. I played a guy who had to go to Iraq at short notice. I guess playing all his games out on time was the last thing on his mind.
When your rating is high you play high rated players giving more losses, forcing the rating to go down. When your rating is low you play low rated players forcing the rating to go up again. Thats why the chart have hills and valleys characteristic.