...Which do you consider more relevant-strict compliance with rules, or effective communication?

I think that to communicate effectively, you have to consider your audience. For example, when writing for pre-schoolers, you shouldn't use university-level words.

Tailoring your writing to your reader does not, however, mean lobbing the rules. The rules were drawn up to help make your writing clearer, not muddy it up.



...Does the writer's ability alter your opinion of the content?

It depends upon what I'm reading.

If I'm reading a paper aimed at the business or scientific community, written in the native language of the writer, yes. If the writer can't be bothered to edit himself, how do I know he bothered to make sure the facts he's presenting are correct?

If I'm reading a fashion or music (pop/rap) piece in which the writer is conversing with his audience, no. The piece is aimed at a specific reader, and the grammar used may be particular to that segment of readership.

If I'm reading a book to entertain myself, I'm not bothered by one or two errors; they can simply be oversights by an editor.

If I keep finding spelling or gramatical errors, it'll irk me though. Too many errors force you to re-read sentences, even paragraphs, to understand meaning. It disturbs the flow of reading.