Thanks to ayeying's testing of a 4 gb module, I bought an 8 gb SO-DIMM kit and installed it in my 2.4 gHz MBP/Santa Rosa. All 8 gb are seen and for the half-hour or so that I've been using it there have been no problems. I notice no performance lag or the such (if anything, it seems a bit snappier). I have not tried Parallels or Fusion, which seem to cause a problem for one blogger. If there are any 64-bit apps available for free or demo that would be a fair test of 64-bit memory mapping, I'd be happy to run them to test the memory. But so far, it sure looks like a MBP - and probably MB and iMac - built on Santa Rosa can utilize 8 gb of RAM.