Not sure if I am on the same page as you are.
I have a Fascinate that I obtained in February with 2.1.1, it updated to Froyo about 4 weeks ago.
I still am able to use the USB connection to transfer files back and forth to my computer. Both with a laptop on Vista 32bit and now with a Desktop Win7x64.
The phone shows a screen with the Android character asking if I want to connect the USB port. If I click 'connect', it does, and then the computer ding dongs and shows me a new USB drive available.
One thing did change. I had to throw away the generic charging cable. I had to buy an extra OEM USB data cable. The generic cable would charge, but no data transfer at all.