I asked payperclickanalyst the same question about Search123 and this was the response I got:
S123 controls the ‘Personal Finance Listings’ text links on Netzero and Juno, just below the Overture type-in search bar.
Everyone.net is a S123 partner who makes its search capability available to their network of partner sites, but it cannot necessarily be seen from the Everyone.net home page.
S123 search results are also distributed to a network of other web sites and meta search engines. Here are a few of the sites where S123 listings are displayed (NOTE> some of these are meta engines which also display listings from other PPC search providers.):
The dealings I have had with Search123 have all been good. But, with all PPC search engines your success will depend on your industry and what you are trying to accomplish. They all have different strengths and search demographics.
I haven't dealt with Search123 enough to be able to say where their keyword and traffic strengths are yet. But I can say that their customer suppport is one of the best I've dealt with.