"The questions are - how fast can I get out of the starting gates with it, and will I start to feel bogged down by its lack of an all inclusuve set of features (i.e. export here, import there, repeat ad infinitum) in 6 months?"

ive been using it for over 6 years and dont feel 'bogged down' by its lack of blo...err.. features. like i said the only thing i really miss is non-destructive deformers like bend... but not so much that i would pay thousands of dollars for them. for the $109 silo is right now you really cant go wrong - even if you switch later on you will still find yourself going back to silo to do quick modeling, or UV mapping, morphs, displacement painting (if you dont have zbrush), etc.  you can also run silo off a USB keyand its small enough so that you can take it and some projects along when traveling and just plug it into any comp and work on them.*