I think this goes along with the issues against modals -- it's something in a user's way, despite how helpful it may be. Which is why the "Do not show at startup" is needed.
Though I've never used Maxthon before, the way it showed tips sounds like a really good idea. It's unobtrusive and entirely optional as to if users even have to pay them any attention.
IMO, it's not good idea to have a feature that has to ask the user if it should "keep quiet." ;)
And, while some tips can seem blatantly obvious, even these tips can still be useful to users that aren't quite as familiar. Those that already know it can just continue on with their day.
