I haven't seen them used much, especially in third party products, but I always wished that back in 2000 we would have had them instead of the owner.

I think they could provide some benefits, and I'd have to work with them more in some larger databases to see. The user of roles to me, has always worked well, and it's eliminated the need to qualify everything. I can see people getting confused with separate schemas, especially if they have different defaults.

My thoughts in the past have been like Jeff's. Use separate databases if you need them, however I do know that there are better tools available now, like Hyperbac and SQL Prompt, to make development easier.