I was already in the same position in a different store, and so I felt that my chances at getting the transfer were pretty good. However, I had been on enough interview panels to know that nothing is ever a given.
[Some people have noted that they were surprised to get emails listing the names of other candidates. This is part of the company culture - there are no secrets about who is applying for what, and who did or didn't get a position. Even the internal announcements of the new hire always thank the other candidates by name.]
To prepare for the interview, I visited the store 4 or 5 times in an attempt to speak to and meet all of the team leaders, store leadership, and the people on the marketing team. This is a crucial part of process and something that outside candidates are not always alerted to - and a huge factor in how the company favors hiring/promoting from within. (In the end, I wasn't able to connect with everyone, but I at least talked to everyone who was on the panel.) I also prepared a presentation outlining my strengths and what I had accomplished in my current position.
The panel consisted of about 10 people, including one person who called in. Everyone else was scrunched into an office, which made it awkward to speak to the group. Making do with limited resources is the norm, though. The interview lasted for 45 minutes, which flew by. As usual, I was asked to make an opening statement at the beginning, and a closing statement at the end. It really helped to anticipate that and have statements rehearsed - those are really your only chances to hold the floor and say whatever you want to say. For the rest of the time, it was the one-way questioning. WFM interviews tend not to be "conversation-y" but rather a series of questions fired at you.
I found out I got the job within a few hours of the interview.