The current version still has the problem that if you do a massive SELECT then it will fill up memory until the process gets killed. In the future we'll give controls to limit how much memory a query can take.
I think it's common in databases that if you throw a massive query at it that the server doesn't have the resources to handle, things will go wrong. It'll thrash, or crash, or generally have poor performance. We'll be working on improving the failure conditions, but if you put a query to a database that is too big for the server to handle, some sort of failure scenario will be encountered. Just a question of how it's handled.
Also, there's no new query planner in 0.10. We have a bunch of work getting merged in for the query engine for 0.11. But if you throw a huge query at the DB that the server can't handle, you'll still have great sadness.
Which DB ended up solving your big query problems? Maybe we're just a poor fit? Or what kinds of queries should we be working on optimizing?