SQL Server case insensitive collation

Question

What are the benefits/drawbacks of using a case insensitive collation in SQL Server (in terms of query performance)?

I have a database that is currently using a case-ins

Answer 1

I can't find anything to confirm whether properly constructed queries work faster on a case-sensitive vs case-insensitive database (although I suspect the difference is negligible), but a few things are clear to me:

1. If your business requirements don't ask for it, you are putting yourself up to a lot of extra work (this is the crux of both HLGEM and Damien_The_Unbeliever's answers).
2. If your business requirements don't ask for it, you are setting yourself up for a lot of possible errors.
3. Its way too easy to construct poorly performing queries in a case-insensitive database if a case sensitive lookup is required:

A query like:

... WHERE UPPER(GivenName) = 'PETER'

won't use an index on GivenName. You would think something like:

... WHERE GivenName = 'PETER' COLLATE SQL_Latin1_General_CP1_CS_AS

would work better, and it does. But for maximum performance you'd have to do something like:

... WHERE GivenName = 'PETER' COLLATE SQL_Latin1_General_CP1_CS_AS
    AND GivenName LIKE 'PETER'

(see this article for the details)