Most efficient way of querying when you do not care about scoring

What is the most effective way to process complex queries ( eg queries with support for negation, and and or, like query_string) when you do not care about the scoring ?

Does wrapping the query in a constant score query give you any benefit.

Or maybe does it make sense to wrap the query in a query filter instead ?

The answers to all of these questions becomes easier in 2.0:

Before 2.0 you are better off using a filtered query and putting everything that you want in the filter, making everything a filter.