Sorry, Australian Context only.
Have read about this on other forums, and put it to the test today. I went to safeway to swap out a sodastream cylinder for a new one. BUT, thought I would ask how much to get a "spare". It seems that there is only one barcode on a sodastream bottle, and when scanned it gives the price for a swap $11.65. The dedicated safeway staff gave it no further thought and handed over the new cylinder without a return, for the eleven bucks. So.... if you like to use sodastream bottles for your kegs, then gettem while they are hot. They will no doubt realise the error of thier ways soon enough.
Only talking the 40 litre ones, haven't tried for one of the 100s. But I might give it a go this weekend. Safeway did it and I have read about the same thing happening in Kmart and Woolworths/BigW