First of all, StumbleUpon does bring traffic.  Is it targeted traffic?  No.  The debate will always linger about the quality and usefulness of SU traffic.  If you are new to internet marketing or just need an extra traffic boost, try it!  Hell, it’s free!  For those of you unfamiliar with SU, I’m, not going to give you detailed instructions on how to use the service.  However, if you need some help, leave a comment and I will respond.

I have found that there are some underlying factors that will affect the usefulness of SU traffic:

Your site’s subject matter
An arcade or funny video site will definitely outperform a Wheelchair Sales site any day as far as conversions are concerned. The comparison is extreme, but use your head when submitting your pages. Otherwise, you are wasting your time.

Keywords, Tags
In order to receive a decent amount of traffic, you will need to research your keywords and titles, otherwise, no one will see your page. Whether you use relevant terms or not is up to you. I use the word “porn” for one of my sites even though it has nothing to do with the subject. But, hey, it works.

Reviews, Reviews, Reviews
If your site has no reviews, it does no good! Make sure that if you are exchanging Stumbles with someone, that they review and tag your page. When you Stumble your own site, do the same.

Your Friends, Your Profile
If you have established PageRank on your StumbleUpon page and are considered to be a PowerStumbler, you will receive traffic to your pages. My suggestion, team up with a PowerStumbler and make more SU friends. Also, ask people to Stumble and review your profile as well as your web pages. Here is a good utility: My Stumble Friends

Deep Links
If your index page is the only page that is Stumbled, your audience will loose interest. Always Stumble deep links within your site. It will help with backlinks also.

This is the short list folks. I am experimenting with timing of Stumbles and cross-bookmarking as well. Here is another useful resource for you: SU Exchange