Daniel Murphy's numbers since moving to first base on May 20: .237/.295/.353 with 4 home runs in 232 at-bats.
Those are not the numbers of a major league first baseman.
I like Murphy, and I'm glad that he's gotten an extensive shot to play first base this summer, but it looks like the experiment has failed. This is not all Murphy's fault, of course - he has almost completely skipped Triple-A ball and probably should've spent the entire 2009 season in Buffalo. Had he failed in left field there and made the transition to first base in the International League, I'd feel a lot better about going into 2010 with him penciled in at first in New York.
For the past few months, I've been saying that the Mets should nevertheless give the first base job to Murphy in 2010 and give him a final opportunity to be a starter at this level. Now, I'm not so sure. If an established first baseman can be had for $4 or $5 million on a one-year deal next season (I'm looking at you, Adam Laroche), he may be the better option for a team that could be forgiven for losing faith in Murphy.
The Mets do not need to sign a first baseman to a long-term deal - and hopefully they will not. Ike Davis has shown potential across two levels this season (.293/.377/.503 with 16 home runs in 392 at-bats). He'll start 2010 in Buffalo and, if he succeeds there, could be the Mets' first baseman on Opening Day 2011.
Murphy may only have six more weeks to give the Mets a sign that he can be the .300/.380/.450 hitter some people think he can be. Now would be a good time to go on a late-season tear similar to what he did in 2008.
EDIT: Dammit, Mets Today beat me to the punch, and it was good enough to be linked at Baseball Think Factory. Click the link and read the article - it's like what I said, but better and more comprehensive.