I'm getting the same thing in 2.48 - Vista 64Bit, dual AMD 9550, 32 GB RAM, nVidia 280 video card.

Just for a comparison I've  tried 2.43, 2.44, 2.46 & 2.47 on the same machine and all are blazing fast. I can sculpt at literally twice the resolution in 2.47 as in 2.48 before I hit the performance wall. Seems to be a definite memory usage problem in 2.48 from what I'm seeing.