It was only supposed to be free through the end of April. But that doesn't necessarily mean that Time Warner is teasing us. As far as I know, there aren't any HD playoff games being broadcast at the moment. TNT, ABC, and ESPN(the regular one) are carrying them.
Yeah, I received a message on my voicemail from Time Warner a few days ago saying I'd be able to see at least 3 playoff games(the last one being tonight's Spurs/Suns matchup) in HD on channel 300 for free. Now if only they can get around to adding ESPN HD and WB HD in the H-Town area.