I don't know if it's really a trend or I'm just noticing, but in the last few years the number of spelling mistakes you find in written pages on the net has increased dramatically. Mostly are due to homophones, which I've started to collect below...
Board / Bored (I have seen this only once, but it's by far my favorite)
Its / It's (very common)
Principal / Principle (common)
Private / Privet (very rare)
Their / There / They're (somewhat less common)
Who's / Whose
Your / You're