Lindajoy I'm with you re the 'should of'. I think the trouble these days is that, although such misuse has been around for decades, we are all on the internet now and reading examples like this on a daily basis. If you hear someone say 'should of', it would be difficult, depending on their enunciation, to be certain that they'd said 'of' instead of 'have' or even the shortened 'should've'. When it's actually in print in all its misspelled glory, we know they've got it wrong and it immediately grates.
And while I'm prepared to accept 'bored of' and 'fed up of' as the natural evolution of language - after all, the prepositions are accepted as perfectly correct when used with similar words, I find it hard to accept 'should of' or 'would of' because it is actually messing with verbal tenses and makes no sense.
Another common error is "Try and run faster". It should be "Try to run faster", i.e. the infinitive 'to run' is needed. This is proved by trying to put this in the past tense: "I tried and run faster"? Sounds ridiculous, doesn't it? It should be "I tried to run faster"