The first derailleur to bear the 'Nexave' name, the Shimano Nexave (T400) was introduced for Model Year 1998. This was the same model year as Shimano's XTR (M951) derailleurs. The Nexave (T400) was frighteningly similar to the XTR (M951), but constructed from less exotic materials. Together the two were the first examples of Shimano's low-normal, 'Rapid Rise' technology. A technology that was much lauded by Shimano, but much loathed by bicycle shop mechanics around the globe.
Like its more esteemed brother, the Shimano Nexave (T400) featured pulley wheels with 11 teeth and a fantastically complicated, sprung, articulating, cable roller to reduce cable friction. Unlike the XTR (M951) the Nexave (T400) also had a 'Light Action' sprung cable clamp. Add in two sprung knuckle pivots and the main parallelogram spring and you have a total of 5 springs in the whole mechanism - possibly a record.
When clean and new, with a well lubricated, and not too flexible chain, tight derailleur rivets and smoothly flowing cables, the whole system worked like a dream. Add in a ladle-full of neglect and a shed-load of filth and you were soon yearning for a little less, low-normal, silky, sophistication and a little more, top-normal, brute, simplicity. The first task of a derailleur is surely to change gear reliably - and no amount of 'Light Action', 'Tap Fire', 'Optical Gear Display', 'Megarange' or any other Shimano buzz-word can substitute for that.