I completed the externship during the summer between junior and senior year, and found it pretty helpful. It can be overwhelming at times (depending on what type of preceptor you get), obnoxious because you aren't allowed to pass medications or chart much of anything (which, realistically, is about 75% of your job), and frustrating because the "journals" you submit aren't always even read by the faculty. Overall though, I feel like the experience gives you a more realistic idea of what nursing is about, and how your days will go on the job. It's especially valuable if you aren't able to work as an aide during your time in nursing school. Don't forget to treat it like a regular job - you have to call in if you're not going to be there or are going to be late, etc. - some people had issues with this and I think it cost them a real job with the hospital in the long run.