Cool, a website especially dedicated to making the distinction between it’s and its clear. This could start something though, how something similar for lets versus let’s? Ah, when to use an apostrophe, and when not to…
And on the subject of apostrophes, this article on their correct usage at Flying Solo.

Typo vigilantes Jeff Deck and Benjamin Herson, whose “work” I mentioned a few months ago, have been convicted of vandalising a noticeboard at a US national park, after noticing it contained a number of grammatical and spelling errors, and then correcting them.
An affidavit by National Park Service agent Christopher A. Smith said investigators learned of [...]

Typo personalities
Apostrophe Man would be delighted with the efforts of Jeff Deck and Benjamin Herson who are men on a mission, a mission to correct poor grammar, wherever they find it.
Picture a pair of Kerouacs armed with Sharpies and erasers and righteous indignation - holding back a flood of mixed metaphors and spelling [...]