TSMC are *currently* the foundry for ATI. The intention was to move ATI onto Global Foundaries this year, which ties in with this news as it sounds like GF are skipping the 32nm node and going straight to this 28nm node. Sounds like 32nm wasn't working out too well, and 28 was.
This will get the ATI and AMD lines both on the same foundry process, ready for integration onto a single die.
I only wonder if, when AMD sold off their fabs, they put in any block on Nvidia using GF as well. They must be desperate to jump ship after the 40nm woes they have had.