According to
http://mining.thegenesisblock.com/, avalon batch 3 (which, if I understand correctly, are based upon the same chips), produce 65GH/s at 620W, or 105MH/w.
At best, electricity costs $0.02/kW*h, or 0.02/1000W*h, so (620W*($0.02/1000W*h)) => $0.0124/h to run 65GH/s, or 0.0124$/h / (65GH/s * 60s/m * 60m/h) =>$0.0000005299/GH. At a difficulty of 100mil, the average number of hashes to solve a block are 100mil * 2**32 => 429496729600000000H => 429496729GH, which means a block "costs" $0.0000005299 *429496729GH => $227.59 but is worth ($130/BTC * 25BTC) => $3250. If the diff increases 60% per month (currently it is increasing at 77% per month according to TGB) then in 3 months it will be 100*(1.6**3) = 410mil, and so on, so I made this table:
If profit is value - electric cost:
today 100mil => (3250 - 228) => $3022 per block found
3 months 410mil => (3250 - 933) => $2317 per block found
4 months 655mil => (3250 - 1491) => $1759 per block found
5 months 1048mil => (3250 - 2385) => $865 per block found
6 months 1678mil => (3250 - 3817) => turn it off, dawg.
Not only does each block net less profit, but we also expect to find blocks slower.
Time to find a block => diff * 2**32 / (hash per s) = time
At 1TH/s, we find:
Today 100mil => 100mil * 2**32 / (1TH/s) *(1m/60s*1h/60m) => 119h to find a block => 0.20 blocks per day => 5.02 BTC/day
3 months 410mil => 0.049block/day => 1.22BTC/day
4 months 655mil => 0.030block/day => 0.7692BTC/day
5 months 1048mil => 0.0192block/day => 0.48BTC/day
So the point is, even 3 months from now, we'd be lucky to be making 2BTC/day, even though it is profitable it'd be better for garr to spend his time deploying hundreds of TH in hardware that won't have to be turned off in just 2 months later. I am unconvinced avalon hardware will be actually hashing in less than 1-2 months from now if we don't cancel the order.
Summary: I was wrong - the avalon chips will probably be profitable to run for 4-7 months, depending on network growth. However, the returns will be so small, I'd still rather bet on future tech, as exponential growth cannot be sustained after 28nm, but we are already seeing 110nm stuff get left in the dust.
The decision is less clear cut, but I still feel like avalon refund is the way to go. We already have a few batch 2/3 devices, right? It's not like we have no avalon hardware, it just seems silly to keep putting money into the old stuff when we could instead put it into the better stuff.
Please correct any errors you find.
EDIT: typos