3D takes double the processing power no matter how it's done. For crappy anaglyph 3D (red/blue/green/whatever) two images are rendered and overlap, with modern methods it takes the frame rate and splits it between each eye which is why people use 120Hz monitors/TVs, 60Hz is what it will feel like.
Awkwardly worded but I think you guys get what I mean.
My point is that current PS3 games are usually capped at 30fps and even they often lag and drop well below 30fps yet we're supposed to believe that Sony will have games magically working just fine in stereo 3D? Yeah right, if they think 10fps (or the feeling of 10fps) is fine, then maybe.