Yes, often times geometry from the 3D Warehouse can be bad, but it is not too difficult to find models that were built in programs other than SketchUp that have decent geometry. The key is to analyze the geometry, and not use (and especially not make many copies of) objects that are junk.
We have had a number of requests in the past for us to host models in FMZ format that can be shared by our users. We have said that we will seriously look into offering this option if enough users post models that they would like to share. (Setting up such a site is not a trivial task by any means and we want to make sure that we are focusing our resources to best benefit our community.) So far, Anton has been the only one (that we remember) who posted models (thanks Anton!) but we need significantly more models to justify the required time to complete such a task.
With regards to dealing with the SketchUp geometry, we agree with some of what Andrew suggests, but here are some specific comments and clarifications related to this:
1. Yes, Separate Faces by Color was a nice feature and we will see if this can be added to v8 in the near future.
2. When running the Object Doctor, first use the Add to Selection option, and Dispaly Results. This will show you all the problems. Use this on specific objects (ie, each piece of furniture, car, person, etc) rather than running it on an entire library of parts. This way you can see more directly what you are dealing with, and better decide if that part is worth using or not.
3. Run the Object Doctor again with the Fix option. When doing this, also uncheck the Missing Faces option (unless you specifically have missing faces you want to repair) and you will avoid the "covering unwanted faces" problem that Andrew mentions.
4. Once you have Fixed the Geometry, the Results that are shown ONLY show what was fixed. If the Fix results all = 0, that does not mean there are any problems, it only means that nothing was fixed. Run the Dr again with the Add to Selection option once more to see what problems still exist.
5. The UnMesh tool (also achieved via the Fix Coplanar Faces option of the Object Doctor) is a safe, easy fix for eliminating unnecessary geometry in a project, but the Reduce Mesh tool is not -- at least not always. We actually removed this tool with the v7 upgrade because while it will reduce geometry, it will (by its nature) also create nonplanar faces, which are not well defined. Triangulating these nonplanar faces will restore their planarity, but doing so may add as much geometry as was removed by the Reduce Mesh tool in the first place, and the results may not be as clean. If you use this tool, carefully inspect the results and make sure that what you have is an improvement in terms of the number of polygons (in relation to the original number), as well as the quality of its geometry.
6. Know when to cut your losses: Yes, if geometry is garbage, then you should either use what you have as a template to quickly rebuild better geometry, or download a different file and see if you can find a file with better results.
7. We are doing our best to find cases where bad SketchUp geometry causes a problem in formZ, and wherever possible, we are adjusting our software to better handle this. Bad geometry will generally never Boolean properly (so don't expect that -- or the Reshape which is a "live Boolean" behind the scenes), and while it may create a bad "local display issue" it should not cause the entire screen to display poorly, or othere such problems. If you ever encounter such an issue, if you can send the part of the file that is causing the problem, we will investigate this and see what we can do to make formZ more "bullet proof" (or garbage proof) for the future.
8. Generally importing files from Revit should work fine (unless they were first built in SketchUp and then imported into Revit). As Andrew notes, SketchUp is notorious for creating bad geometry, and if you look on their forums, their users are repeatedly encountering this problem, and as such, they are searching for new programs to use that do not have this limitation. Fortunately for us, we have been able to convert a lot of these users to formZ users so they can build models that can be utilized throughout the entire design, and construction process.
We hope this helps, and if you have a quantity of decent models that would be useful to others that you would like to share, please zip and send them to firstname.lastname@example.org. (You can also make a post in Tutorials by Users and give a link to these files there if you want to share them with others.) If we do receive a significant quantity of quality models that would justify the creation of a site to host these, we will certainly consider this.