Well over 2000 hours of DC-9/MD-80 instruction/check airman time, both in the sim and aircraft. Very noticable difference in coordination during V1 cuts if the armrests are not used. Found it almost impossible for new pilots to properly control the airplane without the armrests being used, as overcorrections are very noticalbe. Most MEL's are fairly restrictive for broken armrests. When instructing and Checking on the DC/MD series I also look for useage and consider it a "correction" if not being utilized. The initial technique on the airplane for "V1 cut" is pretty much "arm locked, neutral ailerons - initially correct with rudder".
Guess it depends on the aircraft. Jumpseating on various transport jets I always felt that removing the armrests prior to take off was kind of like removing an asset. Basic flying technique shows head movements cause shoulder movements. Locking your elbow on the armrest somewhat prevents this.