My feeling ever since I first used the Tech Preview is that the viewer is a little on the heavy side for DirectX 9 GPUs.
I can understand that the Tech Preview viewer is loading more information into RAM than the old Photosynth viewer, so as to already have images loaded before you get to their position.
And lastly, I know that the Tech Preview is still not fully complete, so I reserved judgement on the viewer for a good while.
Having said that, my complaint remains that for the extremely primitive geometry being rendered, the viewer still bogs down machines that are capable of rendering more detailed graphics at better speeds.
How much hope is there for optimizations to performance?
No offence to Henri. Even Carmack brought in people to optimize Quake.