The anchor text is very important for your ranking in SERPs. I see two reasons to rotate it: 1. You want to target more keywords, 2. Your link seems to be more natural for SEs. Maybe there are more reasons, I don't know.
Yes, I'm also curious about the firefox extension you guys are talking about. I use Roboform and it's pretty cool.
I use fireform as a firefox extension. You can switch profiles on the fly and works not only for directories but article directories and other sites as well. I set up about four or five profiles for each of the sites I am submitting to account for different anchor text. Yesterday, after setting the profiles up, I submitted three sites to a hundred different directories in about an hour. It took the most time just to browse to a category. Use the advanced profiles section for directories submission. Once you have one profile working, just duplicate it and edit it for other profiles, that way you don't have to re-enter the form data that fireform searches for. It's free and a search on Google should bring it right up. The funny thing is I have seen someone selling what would have to be a similiar extension dedicated to directory submissions for about $150.