You have to be careful not to spam yourself - if you self-promote on Digg especially, you can get a good old fashioned "Google slap" -- this happened to me on a website I owned, I was using Bookmarking Demon and wasn't careful enough.
Not only did I get the Google beat-down, but I lost Digg altogether. They can be pretty harsh on that sort of thing. I'd recommend that next time you use Digg very sparingly, and not on every site. If you do use it on every site, make sure you Digg other sites and Hubs, etc., that you do NOT own.
To get your Hub back, do some article marketing to EzineArticles and GoArticles, as well as other high-PR sites. Then link them to your Hub.
Do the same with other web 2.0 properties, like Squidoo, other Hubs, etc. Build backlinks. (I am writing a hub on that right now, in fact.)