We had guesses, but nothing particularly informed. My recollection is that we were right more often than not in our guesses, but it's been a while. We only ran experiments on changes we were willing to make. We never went against conclusive results due to judgement.

We also used data a bit less formally. For example, we had something similar to Google analytics' "funnel" feature of how people arrived at some of our pages, and we noticed a usage pattern that indicated we were missing a feature. When we added the feature directly it was one of our most used features.