I tend to slant towards limiting memory consumption and allocations.  I know it's old school, but:

 - Most of the non-throwaway code I write is heavily parallel.  This means that excessive memory allocation and garbage collection activity will serialize a lot of otherwise parallelizable code.  It also means there will be a lot of contention for a shared memory bus.
 - My primary language is D, which doesn't have good 64-bit support yet (though this is being remedied).
 - I work with fairly large datasets on a regular basis.