Okay, I refined my calculations regarding the power savings that are made possible by the POET AOC compared to copper.
Electricity prices are playing a big role, which is not surprising. In May this year they were as low as 0.0721 $/kWh in Oregon and as high as 0.1586 $/kWh in Connecticut. (No, I won't mention that in Germany household electricity prices are at 0.32 $/kWh, thanks to Energiewende.)
Anyway, the result is that using a POET AOC you would save between $0.53 and $1.16 per link each month, depending on where your data center is located. This is way of from the $10 per watt saved per month as POET states. Perhaps they meant $10 per server per month, which would be in the right order of magnitude.
Here you can check and verify my calculation: https://docs.google.com/spreadsheets/d/1W8xfdlVY4upMM2EchqBoMZZmqPCTGt63YyxSSFJ_7K8/. If I made any errors in my assumptions or in my calculations, please let me know – preferrably by directly commenting in the spreadsheet. Thank you!