Longer contracts make sense IF you buy massive loads of hashrate. For most of us 1 year is the max, but if you have like 50TH/s then 2 years makes sense. The math for much larger amounts is different again.
Though, I'm not sure what to think of the prices. Even with 7% discount it seems like the total return is max 4/5 of the (BTC) investment. So, I wonder what GM was thinking when they started this adventure. There are some trends visible:
1 - Difficulty is high and most, nearly all miners currently for sale are too expensive (in purchase AND maintenance costs) for the amount of hashrate they offer.
2 - People spend their money/coins less easily, partially because of the number of scams, partially because they have become smarter and less greedy and are aware of the previous mentioned trend of hashrate versus costs.
3 - The difficulty increase seems to slow down, which might look good, but it's too early to trust. 5% average is a long way away still, and a drop will not happen within the next... year.
4 - ... Darn. As usual when I have several things in mind, as soon as start writing them down I forget one of them. I'll add it later, when I remember.
All in all I'm afraid that the current offering is not special enough to lead to good sales. Hopefully GM will be able to mine themselves a load of Bitcoins, so no fear of the future. But it still worries me. Companies like GM matter greatly, and I still might buy some hashrate purely to support them and the greater good they offer directly and indirectly.
On top of that another difficulty adjustment is coming within two days which will lift difficulty up another 13% or 14%, making this not the best of times to buy anyway. Since they didn't make it early this week, I actually thought GM was waiting for the beginning of next week, after difficulty adjustment. Guess I was wrong. Which I am, once or twice a year, but who's counting
