The whole hiring and interview process is very laid back, much like the company itself. I applied through the website by dropping a resume and answering a few questions about my availability. They were currently hiring at the time so I was contacted the next day over the phone for a brief phone interview. As I recall, they just asked basic questions about my availability, what area of the store interested me most, whether I personally shopped at REI, etc. I doubt anyone was weeded out at this stage. They offered me a chance to come the next week for a group interview.
The group interview was not like a typical one where you have to compete with each other for speaking time - overall it felt more like a focus group. We sat in a circle and for the first question we just went around the room introducing ourselves, explaining what aspect of the outdoors interested us, and whether or not we had any previous experience in the industry (either in retail sales or otherwise in the outdoor industry). Then we paired up with the person next to us and had to pick an item to sell to our partner (and vice versa). After taking turns doing that, we got back together in the circle and we had to take turns selling our *partner's* item to the rest of the group (i.e., you had to have paid attention to details, even if you had no idea what the gear did prior to them selling it to you). Next, we broke off into 3 groups of about 4 people and went to separate rooms. The interviewer then asked the group as a whole several questions, but with only a few other people in the room it wasn't a challenge to get speaking time. I think they asked something like "What does good service look like to you?" and "How would you describe the experience of shopping at REI?". Finally they gave each of us a scenario to work through, all of which were pretty simple. It would be something like "You're helping someone pick out a tent, but you see someone looking for help in the department next to yours, and you just got paged about a phone call on line 1. What do you do?" (If you can't come up with something to say to that, don't work in retail...)
This took place on a Wednesday and as I recall they called us the next Friday with our results.