Someone somewhere will decide you are cheating and report you. Don't worry about it. Sometimes they will listen to reason and other times they won't. If anyone threatens they will report you, just tell them if they feel that strongly about it to "go ahead, but the GMs have already said multiboxing is OK".

The MOST important thing is that you don't harass them in any way! If they report you for harassment instead of multi-boxing then you will loose. On the other hand, if they harass you, feel free to report them x5.