Just my two cents:
I did not do any externships and while I don't necessarily feel this was the best way to do things, I don't feel like it hurt me in any way. I would have liked to do a month at UCLA and a month at the Brigham but things just come up. Harvards schedule is often slightly different from other schools' schedules and as such you may have to burn 2 blocks just to get 1 month of time at any of the anesthesia programs. (Maybe not though, just make sure to check the blocks at the programs to see if they match up) As for UCLA, I went to school in Boston so to come out to the west coast for a month, get a place, a car, etc was extremely expensive and thus prohibited me from doing it.
Some schools will give you a "courtesy" interview just for doing an away rotation with them, but this is really a double edged sword. If you aren't really competative and you get the interview just for spending the month there, does that really help you? I think one would be better off spending the month at someplace that they want to attend AND someplace they feel that you are competative at.
That being said, a month in a place can give you a much better idea of how things run. It can also slightly skew your views if you get a bad preceptor, resident...whatever. If you have a place you want to go and it won't break your neck or your bank to spend a month there then I would say go. If you have time, go ahead and visit two places, but I would say you do not have to in order to get an interview or to be a competative applicant.
Finally and above all, make sure you enjoy your fourth year....it really is as great as everyone says and since mine is coming to an end I glad I took the time to relax, travel etc (and I didn't burn my vacation months for little if any relative value)
Good Luck
Ca. Dreamin'
PS: See the post by ether on program reviews for 2003 , hopefully there will be even more but there are some opinions of various programs in there.
