Although single content databases of upto 200GB is possible in Sharepoint 2010, administering and managing such a db would be a nightmare. What would you suggest for options in a case where there is one site collection and one corresponding content database. Can you have more than one content db for that one site collection? Can you expand the table to be hosted on other sql servers/machines? Does RBS help?
Here are some details about support for large databases with SP1. http://sharepoint.microsoft.com/blog/Pages/BlogPost.aspx?pID=988
Officially there is support up to 4TBs with optimization, but realistically that is difficult to support and should only be used in extreme exceptions. Technically there were no real changes made to support the additional sizes, it was just an update to guidance. I still try and work with my customers to maintain databases no larger than 75-100GBs unless absolutely necessary. I do have customers with multi-terabyte farms.
A single site collection can only use 1 Content DB. It is possible though to create solutions that use a single site collection that interacts with multiple site collections for content storage. Its transparent to the users, but splits the content across multiple sites, multiple content dbs.
RBS can also help. The big advantage there is it reduces storage within the content db. I'm not as sold on RBS though in most scenarios. There are benefits, but there are also costs and added complexity. If you have an extremely large data source that MUST be in a single site collection and content cannot be archived, then this may be a good solution.
As for multiple SQL servers, you can leverage multiple SQL servers for a single farm, but my understanding is that a single database and all supporting data/log files must be part of the same instance. Using multiple data files on separate disk partitions though is part of the guidance to increase performance on those content dbs above 200GB.
Update: SQL Server Filegroups http://www.sql-server-performance.com/2003/optimize-filegroup-performance/