If you were going to buy an S1, you missed the BEST time to buy was last week, when it went from 1.11 to .998. The price decreases will be a lot less dramatic over the next few weeks I'd imagine because A) They don't want to compete with their own product line, the S2 any more than they already are, and B) $600 is a pretty cheap price when you consider shipping is bundled into that as well. (talking about buying from Bitmaintech directly, do NOT bother with resellers, some of them are great guys, but they exist only because they have built this perception of "It ships from China and it takes FOREVER", which, in most countries, is not the case, and can get it to you in the same time frame as a reseller, or even 1 extra day, but there are lots of shipping problems with resellers, but with Bitmaintech, it is ezpz and enver have had any problems.)
So if you want an S1, pull the trigger today at 0.988, because they aren't going to do any significant price drops until mid-April, you can count on that!
Also, with exponential difficulty increases, expect ROI in about 95-115 days (to be conservative) and as long as you have cheap power in your area, or live in a somewhat tech city, you can resell for maybe 50-70% what you bought the unit for and your "profit" is the resell cost of the miner.
Have fun
EDIT: I used my coupon pricing instead of the actual pricing, because I just bought one at .9... whoops! haha.