Interestingly enough, Windows 7 doesn't really need drive letters anymore.
When I installed the beta, I noticed that while I could see the Windows 7 drive from XP, I couldn't see the XP drive from Windows 7. What I found was that the Windows 7 installer simply hadn't assigned a drive letter to the XP drive. It could see the partition in the disk manager, though.
When I went to mount the drive, I noticed that I had the option of mounting it to a directory instead of assigning a drive letter; I wasn't sure if giving it a drive letter would mess anything up in XP, so I opted for the folder mount; I created an empty C:\XP folder and mounted the drive there. It works pretty much the same as the 'mount' command in UNIX, except that it only needs to be done once; the link is stored in the filesystem, not in a mount table, so when I go into XP I can access XP's C: drive via the vista drive letter if I want to.
It's a really neat feature; the technology has been in NTFS since Windows 2000, but the UI exposure is fairly new (don't know if it's in Vista or not).
As far as the other OS features--process creation, case sensitivity, the backslash--I'm sorry, I can't get on board with you there either. Process creation is something developers care about, not users. The backslash is just legacy UI--if you want to use forward slashes, you can compile Bash for win32. And really, I can't think of a single reason for having a case-sensitive filesystem. "Oh, the reason your PC stopped booting was because you named the boot file 'AUTOEXEC.BAT'. It needs to be 'AutoExec.bat' for it to work."