Darren Rowse at Pro-Blogger has collected Hundreds of Bloggers to Interact with on Digg and StumbleUpon. It's in the form of a bunch of links that you can visit and hit "Add Friend". That's a great list because these are all people who will most likely be interested in your message.

I suppose you could spend several hours adding all those friends and develop a good case of carpal tunnel, or you could just use an Imacro Script to Add Those Digg Friends. It will run through that entire list and click the "Add Friend" button for you.

If you don't have Imacro installed, go do that right away. You can click on the Imacro icon in our sidebar. Then just click the link to the script or download it using right click and run it in Imacro. If you don't know about Imacro, you're about to enter into a wider world.

Some people have expressed reservations in the comments over at Problogger that adding a lot of friends at once in Digg or StumbleUpon could get you banned. I'm not sure what they're basing that on, but our experience from dozens of people over several months is that Digg doesn't mind adding lots of friends. We're the ones who invented the Digg Friend Finder and now the PMS Social Suite, so if banning was going to occur we'd have seen it. YMMV.

Participating in voting blocks and gaming the system will get you banned, that's been documented. Adding lots of friends, on the other hand, is what those sites are designed to support.