i went abroad for my entire junior year and it was the best experience of my life thus far. i was a history major, so i ended up doing my bio and physics req's senior year, pushed off mcat yadda yadda - and im just applying now [hopefully will only have 2 years out]
but if youre going for 1 semester, go for it. it gives you loads of stuff to talk about in your essays, it gives you the chance to explore for a while that you would never get just staying on campus, its a time of more independence and growth. would you be taking the mcat in april then? because as far as apps go, the only thing youd be concerned with that early in the game is studying. but if you take the mcat in april and send in your amcas over the summer, going abroad for a semester wont hurt you at all.
also - as a side note, my sophomore year the dean of admissions at darmouth came to speak to the premed kids about the application process and such. afterwards i was asking her if it would look *better* to stay on campus my junior year and be an RA or go abroad [i was having a hard time deciding between the 2] and she flat out told me to not give a damn what the admissions committees would think, but to do what i was passionate about and that was what would come through on my applications and then impress the committees.
*fewf* ok. sorry for the long post. i just strongly believe EVERYONE should study abroad if they can!! 🙂 hehehe.... good luck!