I'm going to jump in here, I'm a bit late maybe but I have a few points I'd like to make...
1. Microsoft GUI techniques.
Windows is possibly the most inconsistent GUI I have used, it's even worse than AmigaOS - as at least you can configure all the different GUI toolkits to look and operate the same way on the Amiga. There are a few different designs of the window menus - some highlight when you move the mouse over them, some hide items you haven't used recently, some you can even move elsewhere. File requesters are even worse, with several different designs depending mainly on when the program was written, as far as I can tell. In AmigaOS, when asl.library is updated, all the programs using asl.library for requesters automatically get the new look. With Windows, all these old designs still seem to be hanging around. Either everything is staticly linked at compile time, or there are thousands of old routines in DLLs which, rather than being replaced, have been kept - there is some bad design there if they can't just update the DLLs and automatically get the new designs to all programs. Even the XP themes don't extend to the Command Prompt titlebar. It really is a mess.
2. Bringing windows to front with Intuition
I believe OS4 has a feature where you can hold a key down and click on any part of a window to bring it to the front. I think you can do this with old versions too, with the aid of a commodity such as ClickToFront.
3. I like the official OS4 design, I like Simoami's design too but there are more things I don't like about it (why different coloured window gadgets? The screen titlebar looks a bit cluttered). One thing the icons could do with on OS4 is a few more colours. Next to the gradients etc, the GlowIcons look a bit low-coloured. The other thing with the GlowIcons is that the shadow effect should ideally be alpha-channeled so it properly casts a shadow, the design tends to look a bit strange on certain backgrounds otherwise - same with the glow effect. Having said that, I do like GlowIcons and they are much nicer than the sort of rubbish you get on Windows.
Erm, that'll do for now.
Chris