well... I did follow the steps from wiki exactly... Adn no - I haven't seen any of the issues listed there.
When I switched to ubuntu 10.04 LTS - it worked perfectly! Somethin must have changed between Ubuntu 10.04 and 11.04 (and it's not hdparm - which I compiled from sources both times).
Anyway - for anybody looking to secure erase intel 510 ssd on 2011 imac - just use ubuntu 10.04 LTS.