I own bikes both with standard threadless headsets and integrated (also threadless) headsets. The integrated system makes a lot of sense to me. They are lighter, far easier to install and take apart and bearing replacement is a snap. You can assemble or disassemble an integrated headset (except for the crown race) with just a hex wrench. Somebody above said they didn't the system because the bearings are pressed into the frame. That's not true. They aren't pressed at all. The cartridge bearings are simply placed in the widened areas in the head tube. It is regular headset cups that are pressed into the frame. I pressed a Campy threadless headset as recently as today.

The two bikes I own with integrated headsets work and feel just like regular headsets. They have never been a problem nor have I ever spoken with anybody that has had a problem with them. A lot of people fear problems but the problems simply haven't materialized. I certainly wouldn't reject a frame because of integrated headsets.