I figure enough time has passed that we can take a look at how John Jaso has done throwing runners out. CS and SB numbers don't tell the whole story, but obviously you'd like him to be throwing guys out.
April 9: Justin Christian SB(Childers)
April 12: Nolan Reimold SB(Davis)
April 14: Reid Goreki CS(Cromer)
April 16: Reid Goreki SB(Choate), Gregor Blanco SB(Choate)*
April 17: Josh Kroeger SB(Davis)
April 18: Eider Torres CS(Hernandez)
April 20: Wes Timmons SB(DePaula), J.C. Holt CS(Choate)
April 24: Justin Turner SB(Houser), Justin Turner CS(Houser)
April 25: Jolbert Cabrera SB(Talbot), Carlos Rojas CS(Talbot)
*This is starred for two reasons. One, it was actually a double steal, so he really only had a chance to throw one out. But it counts in the stats as 2 SBs against him. Also, he made a throwing error on this play, his only charged error on the year.
So out of 13 attempts, Jaso has thrown out 5, which is about 38.5%. Now, that's a pretty small sample size and I'd be surprised if he keeps that up. 38% isn't outstanding, but it's definitely solid, and it would be a big improvement for Jaso, who only threw out 25.2% in 2008(although he did gun down around 35% in 2007).
Assuming the rest of his defensive skills(ie blocking balls) are at least average, if Jaso keeps his CS% above 30%, I don't see any reason he wouldn't be a passable major-league caliber catcher.