Nice article, thanks for sharing! I find I get a phone screening on <1% of interviews, so the idea of writing a separate cover letter instead of a form letter is discouraging. These are some great tips, though!
On the flip side, I've heard that you should really customize your portfolio for each job as well. For example, if you want to work at Nike, make a Nike portfolio talking about how you're a sneaker head. Then use a similar-but-not-branded "sneaker portfolio" for other sneaker companies you apply to. This may be in addition to a cover letter, but is sort of a blend of cover letter and portfolio.