When to use "i.e." (i.e. How to look intelligent using it correctly)

The Oatmeal explains how to use "i.e." correctly with funny pictures. (You can even order a poster!) [via]
I also like 10 Words You Need to Stop Misspelling. Not that this dyslexic has any right to call out the blackness of any other pots or kettles. But "they're", "their" and "there"?! Com'on people! This is primary school stuff! Yet I each time I marked a stack of essays, I'd inevitably have to go through the differences. And after explaining in class, I would still have kids raising their hand, "Miss, I don't get it, can you explain it again?"
How to Use an Apostrophe is also another important lesson I try to drill into my kids, with varying results. For some odd reason a few of them think that they need to use apostrophes every time they use an "s". I like kitten's, monkey's and zebra's. Before I started teaching in an Australian high school, I had never encountered such gross misuse of the apostrophe. I wonder if Singaporean students are the same.
Don't even get me started on How to Use a Semicolon. I'd be happy for proper commas and fullstops, without run-on sentences; I heart people who semicolon properly.

Humour me: Which do you think is more important - spelling or punctuation?
(i.e. Give me some comment-love, I feel like I'm talking to myself!)

PS I like ranch dressing.
PPS I wonder if I could survive a job as an editor. (Overlooking spelling mistakes aside. Spell cheque can spot those for me, well, mostly.)