The people who had first hand experience using them at MacWorld said they didn't seem slow. Apple said the demo units were using the 80GB hard drives.
But I was concerned enough about it to order the SSD.
I realize, but I wouldn't consider that empirical evidence. There is no question they're going to be much slower than the 2.5" 5400RPM and 7200RPM drives, but the real question will be if it's distractingly slow as it was on the X40/X41 from IBM.