So every 6 months a talk or two from one of the GA's get a lot of buzz on RFM for saying something that might make a TBM question the church or do some research on their own.

For example, a while back Holland went off about Ethan Smith and Solomon Spaulding and so some RFM'rs speculated that some Mormons might actually go online to find out what the deal with these two guys are.

In the last Gen Con Quentin Cook said "some have immersed themselves in Internet materials that magnify, exaggerate, and, in some cases, invent shortcomings of early church leaders..." and some RFM'rs thought this might make some Mormons think who may not realize there's stuff out there.

Does anyone actually know of any Mormons who learned the truth because of something said in conference?

Well, I don't know that I know any.
Of course, it would not come from actually listening to GC because one tends to fall asleep or have their mind wander during said conferences.
It would have to be while reading the written versions of the talks. And we do know that some of those are sometimes 'transformed' before being published. ;)