One thing i know. Dynamic blocks do not export nicely to other software. Even when you explode them. for work that is to be exported, i use designspark (free version of spaceclaim) which exports nicely to sketchup or Autodesk Fusion (also free) that has similar pushpull modeling and exports to STEP/Iges/DWG/Parasolid. Either software could easily model and ellipsoid. and both open sketchup. but dynamic blocks get mashedup a little.

Sketchup is a great application for small structures.
Get the professional version for correct scale layouts.
Sketchup does BOMs and everything else just great.

Ok. Sketchup 7 has some substantial improvements.
What I was really waiting for was real curves. (not faceted) and the ability to export solid models.
I think those features would basically blast a big hole in the MCAD market.
Still Sketchup 7 is worth the upgrade for so many reasons. The dynamic stretching alone is BIG.