I was looking at my logs today and wondering why my uniques had jumped by 20% yesterday and my page views by 35%. By some stroke of luck my site was added to Yahoo! as a free submission. I submit a couple URL's every 6 months but never figured I'd be added, but as of yesterday I'm in. Funny thing is I don't think that I had even submitted the URL that they added.
Enjoy it while it lasts. When Yahoo! adds new sites, you get a "new" tag by your listing and that usually skyrockets your traffic (even more than 20% for me when I was listed years ago) -- it's nice for PageRank and quality traffic, nonetheless.