I do know that, btui still use it. PE5 stop you launching it when sites update their software until they can make sure your use can't be tracked by the site in question.
Think of it like this though. Have you ever been playing live and someone you know has told you about a play or something that someone who wasn't at your table has done? I've seen it discussed at WSOP's on TV between Pros, so how is a HUD any different......
PE5 even changes the stats when the table numbers change later on to take into account how people change their play.
Yes, of course, I've seen it done. You're trying to compare live play and online play, though, and the two are worlds different. Online play, at least for most players, lives and dies based upon stats. "Stories" are part and parcel of live play and you're never really sure they are anything more than just that, anyway.
The more reputable trackers/HUDs collect these stats the honest way and are, therefore, permitted. There are others out there, though, who go above and beyond and deliberately cross into cheating territory by datamining illegally. You'd have to be foolish to be an online player and think sites that do that don't exist and that a certain percentage of players will use them. Maybe they'll get caught, maybe they won't. It's just like the decision you make when you decide to cheat/do something dishonest IRL. Maybe you'll get caught, maybe you won't.... Really it just comes down to personal choice/ethics.