I had a D1 but I'm glad I switched to the Fascinate. Still getting used to the rearrangement of the menu/volume/power button and having no physical keys. I think the most annoying part is not being able to type stuff out while viewing webpages in landscape mode. I hate how the landscape keyboard pops up and covers up the entire screen/webpage....I miss all the extra web viewing real estate you get with having physical keys. I'm finding that I stick to portrait viewing now, which is fine I guess. Was able to get rid of Bing for the most part so thats fine. No GPS issues yet either. Also didn't like the Samsung interface, but Launcher Pro took care of that for me.
Besides all of that minor adjustment stuff I am completely smitten. I was keen on a D2, but after my co-worker showed me his Vibrant I was set on the Fascinate. Its just a gorgeous piece of gadgetry.