I have seen several 9000+ Pligg web sites listings, although almost all web sites about record had been deceased. Would you tell us all which often pligg web sites can you submit the web sites with?
Those with bit of history, following, discussions, real news n info (no spam) + few others that have SE authority (may not have lot of great content)
Most sites running Pligg are a pile of generic crap and/or full of spam. Frankly, the links from there are little to no value. Forget such bookmarking sites and focus on establishing genuine presences for your brand on social sites (mainstream or niche) that have genuine activity.
I used to have a pligg site it got over ran by bots just like the rest of them, i would stay away from them as it could actually hurt your SEO
Most Pligg sites are low page rank and little traffic. There is useless for traffic purpose. However, you still can use them for backlining purpose, but make sure to vary anchor texts because of the Google's Penguin.