Does StumbleUpon work?

I have to say a resounding 'Yes' to that question, but this needs to be qualified by describing exactly what works and in what way.
I have previously stuck doggedly to 'Digg' as my preferred method of promoting blog posts, but have found StumbleUpon to be vastly superior in terms of vloume of traffic generated. Some blogs that I have that would normally get traffic that you can count on one hand, have had traffic rocket up into the hundreds overnight, but whilst this is nice to see - what value is it?
Certainly I have not seen a massive generation of income from this traffic, but nonetheless traffic has to be regarded as good and demonstrates that what you are writing at least captures the imagination of somebody somewhere. Also I have not as yet seen a huge increase in RSS feed reader subscriptions so maybe my blogs do not capture the imagination quite to the right degree...
Nevertheless the proof is in the pudding, and I have seen that immediately after submitting stories to StumbleUpon, traffic has been instantly generated. The fact remains that if I can write some posts that really capture the imagination, I could also increase RSS subscriptions and not have to work so hard promoting the blogs... So far, I have seen traffic fade away very quickly to almost back to the starting point 24 hours later, now I have found a means to effectively generate traffic, I need to devlop the skills to retain it.