You may have seen me say before that it's not worth it to buy the S1, but considering these prices, it might be now(sort of, still too many unknown factors).
I ordered my S1 and paid 0.893, it is Unpaid,Expired but it's due to blockchain.info, hopefully tomorrow it will be resolved.
That's what I figured. Today bitcoin hit a pretty decent low of around $480 (I exchanged some USD at $520) and at .893 BTC that means the S1 was UNDER $500. At the current difficulty, you can get roughly .015 BTC/day. Even with difficulty fluctuations you definitely will be able to make back that .893, it may simply vary between 2-3 months. And at the point you can decide whether to use the BTC to buy another miner, or just call it good and sell the miner on ebay.
A lot of people are speculating that all the 1 and 2 TH miners are going to make the difficulty skyrocket, but I'm not so sure. A lot of farms will remove their current miners to make room for the larger units and/or sell them to fund the purchases. The difficulty will go up a decent amount in the next few months as the large miners ship, but I don't think it will be nearly as bad as people assume.