Hi.. I am also use Propeller and Digg for My site:)
I use the both and would suggest everyone to use both as you can never have too many links, if you know what i mean.
You never know where your potential clients might come from.
both of sites good for traffic and gives best results than others.......
Some traffic does come but not as much as it use to. Besides, now thay both use the "nofollow" att. so no link juice from them.