I’m beginning to theorize that designers and usability researchers can start to quickly evaluate designs with their gut, once they have seen enough usability tests. Watching test after test builds up a body of experence that can result in pattern matching of interface and behavior. This results in situations where a designer (or researcher) looking at a design and feeling uneasy– they might not know why it won’t or will work, but they “know.”
In fact I think the gut is more accurate than a rule.
How to Think With Your Gut lends credence to this theory.