Anyway, here is a breakdown:
Using the batting season finder at baseballreference.com I compared all seasons since 1920 by catchers 24 or under in their first or second season who played at least 70% of their games at catcher in that season. I set the cutoff for WAR at 2.9 or greater and got 15 seasons, all by different players.
Here are the results:
Not a bad list of players to be compared to, all of the players to make the cut since 1989 have had pretty good careers (K. Suzuki is the only one to not make an All-Star team). Posey's season in terms of OPS+ (OPS relative to the league, adjusted for ballpark) is the third best among a 1st or 2nd year catcher. For the sake of brevity, lets compare Posey to what are in my opinion, the three best well rounded (sorry Piazza) catchers on the list; Bench, Mauer and McCann. One thing that does stand out to me is the relative youth of Bench, Mauer and McCann. While McCann had a better 2nd than 3rd year, Mauer had a much improved third season, and Bench improved slightly in his third season before winning NL MVP and hitting 45 HR in his 4th. Let's look at the age 22 and 23 seasons for Mauer, Bench and McCann compared to Posey's age 23 season.
You can see that while Posey's numbers don't quite match up to the 140+ OPS+ seasons had by Bench in 1970, and McCann and Mauer in 2006, Posey does compare favorably to the other season listed included here. And at second glance, McCann played 130 games in 2006 to 108 for Posey in 2010. 108*1.2=130, so we should be able to multiply Posey's totals by 1.2 for comparison with McCann in 2006. If we do that we get 21 HR, 80 RBI, 36 BB and 66 K's which are very similar to McCann's numbers while playing on a markedly weaker offensive team.
What does all this mean? Well, nothing if Posey doesn't make the adjustments necessary to stay one step ahead of big league pitching. It does imply however, that Posey has the tools to be a Brian McCann type player for years to come. If his skills improve from his rookie to sophomore campaign, then that possibility becomes all the more likely. Either way, the future looks bright behind the dish in SF.