When I first installed vista onto my laptop (a Sony Vaio VGN-FE21M) I also installed all the Sony stuff that I needed for it, mainly the VES (Vaio Event Service) and Control Panel, although there is a lot of other junk that they give you to install.
In fact the first thing I did when I had the laptop new was to wipe MCE 2005 off it, and install XP Pro. Now I have nothing against MCE, but there is no point on this laptop; there is no remote, no tuner, and the screen is only 15.1 inches (wide screen), so I couldn't see the point in all the extra paraphernalia that MCE needs running in the background.
When I installed all the Vaio stuff on XP, it all worked fine, as it did in Vista too. Sort of. While the hot keys worked (brightness was the only one I was really interested in), it sapped 50% CPU all the time. This was worrying, as I have a dual core, and thus if I had single core, it would be using 100% all the time. Not good.
To solve this problem, I installed the XP version of the Event Service (Version 2.3.00.08110) instead of the Vista version (Version 3.0.00.13110), which solved the problem, and worked 100%.
Now while I am please it works, it begs the question; if it aint broke, why 'fix' it?. So anyone who's hot keys don't work in Vista, or do work, but slow Vista down (more), just install the XP Versions!