I have a Virus Snow and use Logic Pro 9. In the main I have very few problems, the occasional timing error, but mainly stable to the point where I can write a whole song using all four slots and bounce it down successfully. It occasionally freezes my system, but I can live with that - the sounds on the Virus are wicked and I'm having great fun making patches! 
Maybe it just works better on older gear, as my Macbook is 7 years old!