Hi, folks.
I found your discussion while looking for links back to my Flickr pages. I don't personally use Sketchup but have spent time looking into Google's Street View panoramas. After glancing over the other posts I thought I would offer a few ideas.
I recently posted some additional instructions on how to obtain the 21 images that make up each panorama, including a way to automatically grab them for each stop along driving directions.
If you read the comments under the related images you'll see where I try to clarify to another user that the 21 images make up an already-stitched panorama. This means that Google has already rendered the equirectangular panorama and therefore no need to stitch the 21 images. Instead, just arrange them like a puzzle.
I hope this helps.
-swilsonmc