Sadly, I'm gonna start things off with a question, instead of a tip. Spectere's likely the only one who'll know, but I've gotta ask, why is it that if I leave a video paused in Media Player Classic, at some point, Aero gets disabled, and it reverts back to the default vista colors? And it won't let me change it back till I close MPC, either. It's not an immediate change though, just playing a video in MPC doesn't trigger it, you need to let it sit for a while.
I've never seen that happen on my system, so I dunno. Generally, Vista only disables Aero when your system is running an accelerated application in full screen or when you set Vista to do that using the compatibility settings for a particular application. MPC might be just doing something wonky that's causing Aero to turn itself off.
I just did a quick check, setting uTorrent for a couple different things. "Disable visual themes" did nothing, but "display in 256 colors" did.
You'd need to select "disable desktop composition" for it to have any affect when you're using the full Aero interface. That drops it down to Vista Basic. If you use that in addition to the "disable visual themes" option, that should bring it down to Windows Standard -- yes, the Windows 2000 interface. One difference between the two options is that "disable desktop composition" temporarily disables Aero for all applications. "Disable visual themes" only disables theming support for one application, like XP.
The reason that the "256 colors" option drops you down to Vista Basic is because PC 3D cards can't do 3D rendering (which includes desktop compositing) in 8-bit color modes.
Speaking of compatibility settings, here's a very useful tip for this thread that's related to that.
If you have an OpenGL application that you need to run in a Window and you're running Aero, odds are the application is not going to run too well. This is very dependent on your video card drivers, but generally you are going to see a significant slowdown compared to both Direct3D and, for that matter, a full screen OpenGL application. The reason that this happens is because Aero renders your entire desktop as a Direct3D surface. In order for OpenGL applications to work in such an environment, the calls generally all have to be translated to D3D calls.
To get around this, edit the shortcut for the application that you want to use, click over to the "compatibility" tab, and select "disable desktop composition." Your windowed OpenGL application will now run as fast as it would in XP. You will miss out on Flip 3D, live previews in the ALT-TAB screen, and taskbar window previewing, however, but that only lasts until you exit your application.
Speaking of taskbar window previews, here's a fun thing to try. Make sure that you're running Aero. Now, start up StepMania in windowed mode (make sure to edit the StepMania.ini and force it to use Direct3D as the video renderer, otherwise it may lag!). Drag it off the screen, hold your mouse cursor over the StepMania entry on the taskbar, and play the game using the preview window. It's good fun, I assure you.