I have to clarify this thread - I'm actually a reseller now, for LSS, and it's very good, and very useful, and obviously the 2012 comments above were made before the concept of "NAP consistency" was known.
The process and user interface is similar to Yext, only much better, because unlike Yext they DO take care of the 4 core local data providers like Moz does - (Acxiom, Localeze, Infogroup and Factual)
There are dozens of other valuable directories they list at, (as well as the 'not so valuable' of course), but the full list does covers the spectrum of important sites very well when stacked up against the others.
As a reseller, I can give my client a white labeled login to check progress month after month, and I'm provided with various widget options that runs "local listing status scans" and then captures the lead data into my system.
To quote my rep from one of his emails when I asked - "We absolutely do NOT create duplicates and have several fail safes in place in our workflow to ensure we do not."
Overall, I've found LSS to be a great value and help, and for the end user, it's one of the best values in the industry. Not as cheap as Moz local, but still 1/2 the price of Yext..
