What parameter settings do you use in the X driver? If you haveYes, after setting MaxTapTime to "180" I can drag comfortably. In fact, keeping the default one ("120"), I can drag if I start the drag movement just after the second tap. Maybe I had to play around with the values before and keep from polluting the kernel mailing list ;P
SHMConfig enabled, you can run "synclient -l" to find out. Does
increasing MaxTapTime help?