I went on invis mode almost two years ago, and I wasn't the first to do so. What's taking you so long?
I played WW quite a long time and never felt the need for going to invisible. Why, you may ask. Well, the answer is that because I'm a man and not a mice and I don't hide in the shadows. Whole invisibility mode just and constantly peeping other player's activities outside the WW thread has always felt like cheating.
So tell me my friend why some people need to use invisibility mode and be peeping toms? My opinion is that they need such gamey methods, because they can't win in honourable ways. Using forum's flaws against others is bit like abusing all AI flaws and game mechanics in EU3 multiplayer game to get advantage against your human opponents.
Never came to my mind either, because spying the GM is even more outrageous idea.