The results of dynamic prop balancng are a benefit to the engine and
airframe.  If you still FEEL vibration, check for anything on the engine
touching the airframe.  Also, remember that if you are using a 4-banger,
there is inherent vibration - if a 6-cyl, optimun engine smooth, etc.  Marv
would argue that every thing should be spinning 'round and not beating itself
back and forth.  If you still don't like this, consider a harmonic dampener.  
IPS numbers are best if they are small, the rest is up to you a$$.

Grayhawk
Old guys are smooth because they're harmonically dampened!