I was just signing up for a conference, and the registration form had a couple “usability” problems.

First, it asked me for my zip+4. I don’t know what it is. I had to get a piece of mail addressed to me to find out.

Why would you do that? How many people actually know their zip+4?

Second, it asked for my fax number. Again, I don’t know it off the top of my head. I have to consult my business card.

Third, there was no indication of which fields were required and which were optional, so I didn’t know if I had to go look up my fax number.