Beryl has a lot of plugins that you can play with, some of them are maybe very experimental but I think this project will be big in the future. I haven't seen much about Vista aero but I think, Beryl has to nothing to envy. Mac users would say "deja vu" but this is linux, free and open source and surely it will become something very interesting.
I must say that I thought the process of installing Beryl would be very frustrating (it's just 0.2.0 version), but it just run flawlessly at the first try (following this how-to wiki ). Now I use Beryl as the default window manager, it's running smoothly so far. I think it's all about the video card and the driver, I have an nvidia GeForce 6200 using this driver and also with it you can easily set the dual monitor configuration ( Xinerama ).
I tried to capture my two screens using Xvidcap but to get a decent frame rate all I could capture was a 40 x 40 pixels frame of the screen :(. Instead I used my camera pointing to one monitor and this is what I got:
