On the website it says you can use 1 hard drive but you'll need to format it and update the PS3 every time you change the FW. I don't think you'll lose any saved data though.
Well it depends on what team E3 meant by formatting. But know that you mention it I think you will loose your saved data.
I would get a 2.5 GB harddrive for CFW to keep all my games on it, and use the original internal HDD for OFW. I'll do that or use a HDD from one of my old fat YLOD PS3s.
Just in case anyone wants to know the Nor solderless 360-clips are now available. So you know, you need a progskeet 1.1 or 1.0 with the added 50 pin zif connector. They run about $50 and they are a good grab if you want to dual boot solderless. (now if only they can release the dual nand adaptor life for me would be grand)