Computing sums of the columns of an array

From: Martin C. Martin

Hi,

I have a 5x731 array A, and I want to compute the sums of the 
columns.  
Currently I do:

apply(A, 2, sum)

But it turns out, this is slow: 70% of my CPU time is spent 
here, even 
though there are many complicated steps in my computation.

Is there a faster way?

Thanks,
Martin