I found this through reading Mike Peatzold's Word Press Made easy Blog

Stumbleupon or DIGG?
So, you have a great new post, one you feel others will surely appreciate. How will you call attention to it, StumbleUpon or Digg? Both have the potential to send huge amounts of traffic your way, but is one better than the other?

StumbleUpon
StumbleUpon is a very cool social networking and bookmarking site. The premise is simple, install the toolbar, click the icon to surf, and give the thumbs up sign to the blogs and websites you like. Submitting your blog in this manner will enter it into the StumbleUpon queue. Now other Stumblers might come upon your blog through their own surfing.

The more Stumblers giving your blog the thumbs up, the more traffic you will receive. Many sites and blogs receive thousands of stumbles in a single day thanks to member approval.

The thing to remember is that large bursts of traffic can be short lived. While you might see flowing traffic from StumbleUpon for a good week or two, after that you might get only a stumble or two here or there. The good news is that you more than likely landed a few new regular readers. Super Stumbles might not happen often, but there's a good chance you'll continue to receive traffic from StumbleUpon weeks after submitting your blog.

Digg
Digg is a whole other ballgame. Like StumbleUpon, it's a simple premise. You submit your article or blog post to Digg in hopes of other"

Digg traffic doesn't last long, however. If you receive lots of Diggs, you might see traffic for a few days. If you only get a Digg or two, you'll probably only see that many visitors. Unlike StumbleUpon, where your blog may continue to turn up when Stumblers surf weeks later, with Digg, the more time that passes, they less likely it is for someone to come upon your post.

Which is best for your blog?
Both Digg and StumbleUpon have their pros and cons. If you can submit to both, by all means do so. You're sure to get some traffic as a result. You have a better result of being Stumbled than Dugg. Since StumbleUpon allows Stumblers to visit random sites, the chance of someone landing on your blog is a lot higher than if they were to find it on Digg. Unless you're in the top couple of pages, most people won't know you exist.

Test them both out to see what works best for you. Both Diggers and Stumblers love to share great content. Give them something to talk about and submit to both.

Article By Deborah Ng found at About.Weblogs Through Mike's Blog