For me StumbleUpon is hit and miss with its often dated results and submissions intended solely to drive traffic. The secret weapon of Pu.ly is that your "pulls" can be displayed based on your Know About It account. As stated in the previous review of Know About It's service they scan your social accounts and content subscriptions to email you "recommendations to the next level with intuitive analysis of multiple data sources to truly show what you want to see, not just aggregated stories that were shared the most".
They built Pu.ly's discovery engine on top of that platform to show you random content that is interesting to you. Using their algorithms and the mountains of user data they have about what you and others like you like they bring relevance to a new level. Most importantly it is fresh and recent content, with the majority coming from your social streams. While using the service when logged in and linked with Know About It you can see what people in your social circles are saying about the pulls via the chatter button and also share a pull directly to Twitter and Facebook.
If you prefer, or don't have a Know About It account, you can still "pull another". The results will still be timely and interesting, just not personalized to your interests. The service is new and will certainly improve over time. A good feature to add would be to incorporate a yes/no button to further gauge a logged in user's interest in the displayed item; another would be to have the ability to toggle on/off sharing to specific networks.
Give Pu.ly a try today and share your thoughts. I highly recommend you set up a Know About It account to enhance what you are shown. Today I will be pulling stories and not falling all over and stumbling while I look for good things to read.