A mix, as 'true' taichi probably should be, the basic philosophy being (for those of you happen not to know) that it's a spin-off from kung-fu (so a fighting style) but one focused more on concentration and sensetivity to the enviroment and opponent than strength and dexterity ('inner voise'). But in terms of what i'm being taught at this particular class it's more focused towards 'inner voise'.
In that sense it's not nearly as good of a work out as somthing like Karate or Kung-fu, it's easy to go through a two hour session without even breaking a sweat because everything is done so slowly. However, it has been great for my energy, coordination, and, most importantly in the context of this thread, my flexability (in terms of my muscles not all being stiff from too much working at a computer).
To supliment the lack of 'real' workout from this, I just run up and down the hill to campus.
So to answer your question,