"Generating dSYM file" takes ages in XCode 4.5

Every time I build in XCode 4.5 I note this step takes over a minute, in a full rebuild this step is probably as long as everything else in total!

I previously used XCode 3.2.6 and building in 4.5 is far slower. Is there anything I can do to improve this? Is there any information on what a dSYM does, I don't recall ever seeing it on 3.2.6.