How many mastery points does it take before you can actually be considered good with a champion?

I know this tends to vary based on the skill-cap of your champion, but I'd like to know what people think in general. I do like the mastery system (with the exception of the recent additions) in some respects because it lets me keep a running tally of how much I play specific champions and gives me a general idea of how much I know about them.

But how far does it go? I guess what I'm asking is is champion mastery really an accurate representation of skill. I know people with over 1 million mastery points on a champion, and there's no doubt they know that champion well. But then I see people on these forums boasting about their 100K mastery points and thinking they've got their champion all figured out and know what they're talking about.

Personally I've always thought that the requirements for getting mastery level 5 were a bit lax. You can easily get mastery level 5 with just a few dozen games, but it takes far more than that to truly know everything a champion can do and even more than that to actually be able to translate that knowledge into gameplay. For example, my highest mastery champion is Shaco at 333K and I STILL don't have any illusions about having mastered Shaco.

Does riot's mastery system actually indicate skill, or does it simply give a rough idea of quantity of games with a champion?