I went for 64-bit mostly because I bought student copies through the Microsoft website which let you purchase one 32-bit and one 64-bit version (I had already used the 32-bit). From what I remember it was a clean install, it had come with Vista and had no files that I'd need so I'm 99.9%...
As the title says, when I restart my laptop (acer aspire 3810t, upgraded from Vista 32-bit to 7 64-bit) files that have been recently edited/accessed will still be on the hard drive, although appear as 0 bytes (I'm not sure whether they are still using the same space on the disk as the problem...