Ben,
I have the same experience: hit and miss. I finally though I found the way to submit to all my friends at once (right click on one of my favorites) but that resulted in an email I sended out to all friends. I had some traffic from that, but mainly you guys visiting me
(It could also be thay you all thought the article wasn't worth a review (which of course is totally valid as I also will only stumble and review if I like something).
Another thing I noticed is that SU traffic comes in waves. You hit a peak and than it slows down and stops.