From my experience and freelancing from company to company here in Los Angeles.
I seen alot of companies use Combustion for roto. Even the company(DD) that I am at now, they use combustion for roto.
and this is for high end movies, and commercials.
I used mattes from Combustion and they are perfect, and plus you can export splines out as a Gmask for other programs like flame, inferno, and AE to use....I don't know if you can import a Gmask into shake.
I'll ask the roto team about more info on what they perfer instead.
i'll get back to you, russ