none,
I think your question is a very good one -- I asked it too. UCI was the only unranked school to which I was accepted, and yet I still ended up going there. It was a very difficult thing. You can say that rankings don't matter, but in the back of your mind, you always want to go to the best school you can -- best in your eyes and in the eyes of others. For me, there were alot of other factors which I had to consider. At first I thought that I was choosing a school which was not quite good enough, but after half a year at UCI, I can really find nothing wrong with it, and in fact, I have a great deal of respect and admiration for the students and administration. I think that UCI is not ranked because of the fact that it is the newest UC, and the smallest. I have a feeling it may move up in the near future. But the students are really bright and there are alot of opportunities to anything you want in terms of research, clinical experience, political stuff, community works, etc... Even first years in my class have already received grants for starting community clinics. I know one second year guy who is taking classes, doing research, and is getting a book published!
Now I hope everyone knows that I am not bragging about UCI, but just giving some personal thoughts and observations. The bottom line is that it is a good school despite the fact that it is unranked. It isn't a Harvard or Duke, but between the opportunities, the board scores, and the beach, I, personally, am very happy that I chose it over others (including a certain northeastern school ranked in the top 10.)