We just came through immigration here in AR for the first time this week. No one asked us about proof of return ticket. Or about anything really, although the Delta gate agent in Atlanta did check for proof of payment of the reciprocity fee. However, I will say that we spent a LOT of time worrying about the possibility of being denied entry onto the plane prior to our departure. This is mainly because of what we had read on blogs and websites about the 90-day issue. Also, the travel agent I was required to use by my employer refused to purchase a ticket of longer than 90 day duration because of the policy/requirement (whatever you want to call it). She was so difficult we purchased the remaining tickets for my family privately and then also purchased one-way tickets to Montevideo to show as proof of exit if asked. So, if it is a "scam" as some here have suggested, it is a systemic problem--going the whole way back to US travel agents. We weren't willing to risk it.