Rhino's native sketchup export is not at all good, and will hopefully get a tune up before too long - it is likely it will be posted on the rhino labs page when they get around to it.
In the meantime, try using these settings for a dwg export out of rhino, which i have had pretty good results from:
I model in rhino in mm with a tolerance of .1
Autocad version - 2000
save curves as - splines
save surfaces as - polygon meshes
save polygon meshes as - polyface meshes
curve options - use simple entities
simplify tolerance .05
polygon mesh detailed options:
as per model settings, which should be everything set to zero except max distance, edge to surface = 2
check refine mesh
check simple planes
in sketchup import dwg settings : millimeters, merge co-planer faces, but uncheck orient faces consistently as seems to come from rhino fine.
The other way around this is to buy moi, and then immediately download the v2 beta, which has an absolutely fantastic sketchup exporter. Moi will open rhino files natively, and you can actually cut and paste between rhino and moi. - in fact, moi is coded by the same guy who originally created rhino; i just consider it a rhino plugin - it will pay for itself on the first job or two....
cheers
rabbit