Well.. first why would you do that? 2nd.. No its not a turn on.

I can't really think of any positions that you wouldn't be able to do wearing boxer briefs... but I do think that it's not as comfortable that way. I've had sex with regular boxers on and even with them being lose (as opposed to boxer briefs) I think it's a lot less restrictive without anything.

Although I'm curious, why do you wear them during sex?

unless your scared of getting caught and wen some1 walks in and you want to scramble and put ur clothes back on as quick as possible, i'd be bare naked!! its hell sexier, more intimate and not as hot! however i dont think its a major turn off for women, but i dont ever really do it.