Ankh-Morpork Guard said:
Nothing major HAS been nullified by the movies. Not even the clone use in the Thrawn trilogy...as that was obviously using a different method than the Kaminoans do. In the Thrawn Trilogy, Spaarti Cloning Cylindars were used, and those didn't have nearly the same kind of success rate that the Kaminoan ones did.
Honestly, the only two things I can think of that have been downright nullified are Boba Fett's background(which had four or five different versions anyway) and the details on the Death Star's construction.
Even then, only some of the details of the Death Star's construction. It's still perfectly feasible that Tarkin had his little secret Maw facility working on a lot of the technical problems the Geonosians didn't work out or places where the Empire thought they could improve upon the design. The basic idea that the Death Star's operating philosophy was the Tarkin Doctrine, to rule by fear of force rather than the use of force by presenting such a powerful weapon that no defense is possible is still valid. Building it in the Horuz system, over Despayre is still valid, and the secret Maw installation in the Kessel system is still valid as a place for some early prototype work and R&D on the design.
Also, note that the Kaminoan clones did take some quite som time to grow and mature, just like Spaarti grown clones (without Yslimiri help), the movies never implied that you could just pop out clone armies with the push of a button. Spaarti technology may be a different implementation than Kaminoan cloning, but the basic ideas don't contradict.
In general, I think the prequels were quite kind to the EU in not contradicting anything major. Even the controversial Dark Empire series was supported by Palpatine's declaration that he knew a way to cheat death (I know some people hate DE, but right there in the movie he says he knows how to cheat death, and the believed-dead villain returning is a staple of pulp adventure, which Star Wars tries to be). Only Boba Fett's backstory (of which there were already several conflicting stories) was really ignoring the EU.
The Prequels actually took a few things that were originally created for the EU and made them Canon. The name Coruscant was created by Timothy Zahn for Heir to the Empire and the rest of the Thrawn novels, and Lucas decided to adopt it (replacing his original idea of calling the city-world capitol of the Empire either Jhantor or Had Abbadon). Some fans like to look down on the EU as not canon (which by the strictest of definitions, it isn't), but Lucas himself is well aware of what's in the EU, the general direction things take, and he has exercised veto power over plot developments he disapproved of (Joruus C'boath was originally going to be a clone of Obi-Wan, but Lucas said no way). The EU may not be strict canon, but Lucas paid attention to it in creating the prequels.
