DLL Hell: What are you doing that requires you to mess around with DLL files? I’m always in the guts of my system and rarely have to mess with this.
The Registry (and the all too frequent necessity to muddle with it): How frequently and why? I’ve hit up the Registry my fair share of times too, but only for special circumstances, and since Windows 7, it’s incredibly rare as well.
Drive letter assignments (instead of proper UNIX arbitrary mounting): Completely agree with this. This is archaic and needs to die. I’m sure Microsoft only keeps it because it would otherwise be a huge compatibility break.
The Ribbon/Aero (talk about sloppy overwrought chrome): I don’t really see this as a problem. I think Windows 7’s interface is actually kind of nice.
Convoluted control panels (or bafflingly absent ones, like NTP setup): OSX’s System Preferences is only marginally better IMHO, though Windows 7’s customized control panel interface can make it really hard to find stuff. You can turn that off and basically make it look like OSX’s though.
Ugly screen fonts: Never noticed this.