My answer to that question is, "yes, that appears to be the case."  Lance Berkman started off the season with a disappointing couple of months.  However, Berkman's offense was nearly normal in May and has been great in June.  Berkman's OPS by month in 2009:

March/April  .718

May  .918

June  1.014

Lance Berkman's current OPS is .885.  It seems like many fans, remembering the bad March and April, are stuck with the idea that Berkman is having a terrible season.  An .885 OPS is not terrible.  While it is lower than we expect from a player of Berkman's caliber, Berkman's current OPS is quite good for most players.  His OPS currently is higher than a number of fine hitters who are reputedly having good or at least normal years, such as Ryan Howard, Casey Blake, Ryan Zimmerman, Carlos Lee, Derek Lee, and Matt Kemp.  Moreover, Berkman's offensive performance is within his normal range for two of the three monthly intervals, and is showing a definite pattern of improvement.

On another board, a fan raised the idea that Berkman's offensive problems rest with his performance against LHPs this season.  The proposition was offered that Berkman is showing a deteriorating ability to hit LHPs which is some type of symptom of age-related decline.  So, let's look at the platoon split issue.

As an initial point, we know that Lance Berkman, over the course of his career, has always had a significant platoon split in favor of hitting RHPs.  On a career basis, Berkman's OPS off LHPs is approximately 200 points less than when he faces RHPs.  Berkman's has the OPS of an average hitter against LHPs and a superstar OPS against RHPs.  And it's true that Berkman's offense against LHPs this season is particularly poor, with an OPS disadvantage against LHPs of more than 300 points.

However, something people seem to forget when looking at batting splits over a partial season is that sample size is always an issue for the LHP side of the split.   Berkman has only had 75 plate appearances against LHPs this season.  You really can't draw any conclusions about OPS or batting average for that size of sample.  So, I can't buy into the idea that Berkman's offense is declining this season because he has a drop off in his fundamental ability to hit LHPs.  I also wouldn't be surprised if the results of Berkman's offensive improvement take longer to materialize against LHPs due to the sporadic number of plate appearances against LHPs.

Is Berkman's poor platoon split this year evidence of a deteriorating trend in hitting LHPs?  No, I don't think so.  Berkman's OPS versus LHPs in 2008 (.803)  was higher than his career OPS against LHPs and produced an OPS gap of less than 200 points  between the left and right side.

One noteworthy aspect of Berkman's platoon split so far this season is that he has been drawing few walks against LHPs, which weakened his OPS results for that side.  On the other hand, Berkman is hitting HRs equally well against both LHP and RHP this season.  The following rates are shown per plate appearance:

Walks/PA

2009 vs. RHP  21%

2009 vs. LHP  5%

Career vs. RHP 15.8%

Career vs. LHP 13.6%

HR/PA

2009 vs. RHP  5.5%

2009 vs. LHP  5.5%

Career vs. RHP 5.7%

Career vs. LHP 2.6%

The K rate versus LHP and RHP this season isn't too different from his career ratios.   Berkman is hitting HRs at a higher rate versus LHP, and about the same rate versus RHP, which counters the idea that he is suffering a major decline this year.  But Berkman is taking significantly fewer walks against LHPs this season.  That could be due to: (1) problems seeing the ball batting right handed; (2) a change in pitchers' tactics when he bats right handed; (3) impatience by Berkman when he faces LHPs this season; or (4) just a fluke of sample size.  My money would be on No. 4, sample size.  But it's worth keeping an eye on this season.