Our clinicals assigments were based on the process that Nurse Salt described. There are 3 alphabetical groups, and each group gets a chance to be 1st during one of terms. The registrar sends out a list of the clinical sites and times, and can request your 1st, 2nd, and 3rd choice. Even though you are in the first priority group, you may not get your 1st choice if it's really popular clinical site. The registrar randomly pull names from your alphabetical group, so even if you are in the 1st priority group you are still competing w/ 16 (or so) other people for the choice spots.
All that being said, I've heard they may revise the process for next year. The ABSN director talked with us a few months ago and said it will be changed but they haven't worked out the exact details yet. \
You will most likely have a weekend at some point in time. Like Nurse Salt said, most clinicals are only for 5 weeks. This time 2 of our back-to-back clinicals were weekends, so that's why I'm stuck w/ 10 weeks of weekends. Anyways, time goes by fast so it'll be over before you know it.