Usability research on sticky headers?

Sticky (or fixed) headers are not so uncommon nowadays, and for a large website that relies heavily on catalog and search functionality it may be a good choice to aid the user.

As I am currently designing such a website, I was wondering if there was any research done on how users re-act to them? Of course it all depends on how you implement it, and how savvy your user base is, but is there any research-based pattern information available? Common pitfalls, best practices, etc?