A thread at WebmasterWorld asks What happens if we stop paying for Site Match? In response to that we have two replies (I have no experience with this, so I can not comment on its accuracy).
We got screwed both ways. We had a bunch of sites that were anywhere from #1 for 2yrs and mostly top 8 sites in many areas. Joined site match in hopes of maintaining positions, ALL sites disappeared almost instantly. We cancelled site match and NONE of the sites have returned to index must less prior positions. Go figure.
Ditto. I would love nothing more that to be able to preach the glory of how great Yahoo is, but no-can-do at the moment.