I am having a serious traffic problem. My website capped at 40 uniques a day and it's being going downhill since then to about 18 and it may even go on further down. I submitted the sitemap to Google through webmaster tools last Friday, and it says "4,191 Submitted / 2,603 Indexed".
Why aren't they all indexed? How can I find out which ones aren't?

I've been reading about the big broohaha over the Google updates, could this be what capped my traffic?
I have about 12-20 updates a day, I have SE friendly URLs, perhaps I should be using black hat, I'm feeling a little discouraged.