I have been rolling it out. Great job! I am not having any problems. I installed the RA Server and Console over the top of the old... Next... Next... Next... done deal. I have installed the 4.2 client over the top of 4.0 and have been running it on several machines some new and some old and have not had a single issue so far. All good here!
I've been historically fearful of installing it over an existing install. I've done it between the 4.2 builds recently and also have experienced no issues. I guess it would only be a no no between major versions. All in all Eset has the best installer/uninstaller of any AV in the business IMHO and experience. Yet another reason to love it!