I did the Chicago Ragnar last June and it was a lot of fun. Getting a team together and having lots of alternates ready to jump in if an original team member drops out is key. I have done 4 relays (only one Ragnar) and every team I have been on has had at least two runners who committed in the beginning and were forced to drop out at the last moment.
Also you need to make sure the team you have has runners committed to the training and have at least a solid year of running--at least 6 miles or more-- ready to go.
And lastly, if you commit, get your vans reserved and try to have a non-runner be your drivers so your runners can get as much rest as they can without having to worry about driving to the next exchange.