I thought I would post my response to someone who asked me to elaborate more on my above post in a private message. I think there may be others who would like to hear what I told him. The basic question was that he had heard it was a good thing to do a SubI so that you could get into a program more easily and obtain a letter of recommendation. My response to him is as follows.
No problem. I really meant what I said. I think that away rotations are useful for the following:
1 - they will definitely help you understand what other programs are like. Even if you don't interview at the place you subI (that's rare, usually they invite you at least out of courtesy unless your scores are terrible) you get to know what life is like outside your home school.
2 - if you're truly interested in one program you can really learn a lot about it and whether or not it is the place for you by doing a rotation there.
However, consider this before going
1 - You have to be better than perfect on your rotation. And you are walking a fine line by doing so. For example, if you are too aggressive, residents will find you annoying. But, if you slack even a little, you can get a bad reputation as lazy. In either case, on a rotation, attendings will have some but not great contact with you. Your reputation will be built on how you work for the resident team and the residents will determine your worth to the program. DO NOT UNDERESTIMATE how much the residents will make or break your subI evaluation and or your reputation to the admissions committee. This can be difficult because you might get stuck with residents who are not getting along on thier team and just are unhappy before you get there, who have a bad chief, who do not care about you (unlikely), who do not share anything in common with you, who just don't mix with your personality, etc.
I cannot overemphasize this point either--know your stuff, but keep your place. Do not try to outshine your residents. Do not volunteer an answer to a question that a resident cannot answer unless you are asked to do so. That's suicide. Your #1 job as a student is to make your resident(s) look good. (Just as a resident's job is to make his chief look good and the chief his attending.) You do that and the attendings will hear about how wonderful you are. You do something to make the resident(s) not like you, especially a resident who the staff likes, and you just cut your throat.
This may seem like no-brainer stuff to you, but from what I saw it's not. The social skills killed subI's so many times. All of them were bright, but many just didn't get it. Make the resident look good, you're golden. Another example: know every lab, every vital, every radiograph result, etc so that you can make sure your team is aware. I would sometimes give signs (without the attending seeing) to the resident getting pimped about things like that which kept them out of trouble with the attending which then got me ridiculous praise.
2 - a study showed that for SubI's in ENT, the chance of matching at the program through which you rotate is not statistically improved by doing the away.
3 - if you go on an away, sometimes the school will ask if you want to do your interview while you're there to save you money from having to come out again. This has one of two implications. Either they hate you and they're trying to interview you now so that they don't close a slot for someone else on the regular interview day (and are just being nice by giving you the interview). Or they absolutely love you and want you there no matter what. Unless you are 100% sure you are in the 2nd group, come back for an interview if that place is where you want to go. If you interview early, you will not get equal treatment at the ranking meeting with the others who come.
Overall, I think you should go on a subI. I wouldn't go to a place where you really wanted to match, unless you are absolutely sure you can be the best thing they've ever seen. Remember, you'll likely be there with at least one other subI too who may make you look either brilliant or ******ed. And unfortunately, you won't know until you're there.
My opinion regarding getting letters from attendings at your away is mixed. Mostly, I find it stupid. Who is going to read that letter and think someone who knew you for a month has any in-depth knowledge of what your chances of being a good resident are? At one of my SubI's, an attending, now the current chair, said he'd write a letter for me. I thought that was awesome and was quite flattered, but I told him I had already submitted mine. Not entirely true, but I really thought that him knowing me for a month was not nearly as good as my own department knowing me for the better part of a year.
That's my 2 cents. Hope it helps.