The super prospect Oriole catcher has not yet played a major league game. He is projected to hit 274/352/439, which combined with strong defense behind the plate makes him already one of the 30 best players in the game.
And that's just going on my projection, which is the most pessimistic among those that I've looked at. Most systems have him around a .380 OBP and .480 slugging, which probably puts him in the top 10. Those projections aren't enough to get him a big league job as the Orioles will send him to AAA for service time reasons.
Having such a low projection on him makes me wonder if I'm missing something, so I looked at the best hitters I could find in the Eastern league who had at least 200 AB there and were age 23 or younger (Wieters was 22). By OPS, they are:
Ron Kittle, 1981 1.119
David Wright, 2004 1.086
Wieters, 2008 1.085
Nick Johnson, 1999
Pat Burrell, 1999
Vladimir Guerrero, 1996
Sean Casey, 1997
Scott Rolen, 1996
All of these players had an OPS of at least 1.030. Kittle went to AAA the next year and hit 50 homers, then won the 1983 rookie of the year award for the White Sox, hitting 35 homers, but lack of ability to make contact prevented him from doing much else for his career. Nick Johnson got hurt (duh) and missed the whole 2000 season, was less impressive in AAA, mediocre as a rookie 3 years later, but eventually proved to be a great hitter in between DL appearances.
The other 5 played in the majors the following year, and on average posted an .839 OPS. They all were able to improve on the rookie numbers and range from outstanding hitter for brief periods of time (Casey) to HOF level hitters (Vlad, probably Wright). That bodes well for Wieters, but it's probably not a good idea to expect the 900 OPS right off the bat.
The 791 OPS that my system projects, however, might be a bit low. Wieters hit better in AA than he had at a lower level. Nick Markakis did the same a few years ago. David Wright's AA performance was way better than his 2003 season in the Florida State league. Perhaps players who show abnormal improvement when jumping to AA should be looked at a little differently.