I use the Omega drivers a lot on my Envy M855 notebook because ATI's drivers don't work by default with mobile chipsets. In the past, I ran my desktop with ATI's official drivers and the notebook with Omega's, but it became to much of a hassle to keep both drivers up to date. Especially since my notebook has evolved into my primary gaming machine. So far, I've found the Omega drivers to be reliable, on both my systems, however, I've never ran on comparison benches between official drivers and Omega.
Would be nice for AT or FS to do a comprehensive benchmark suite between the ATI/Nvidia official drivers and the ATI/Nvidia Omega drivers though.