Not only is it the most important skill (unless for small home projects maybe), it's also the one which takes the longest to learn and hence the one you really improve on during the years and which distinguishes the experienced ones from the lesser experienced ones. Coincidently, it's also the skill for which you won't find a ready-made answer on stackoverflow or any other site/book.
thinking of it, I've also seen this as a typical difference between fresh CS graduates and those who have been programming for 10+ years. The latter would sometime take way longer to come up with clever math-oriented algorythms than the first, because the graduate has been trained for it and still has it fresh in memory, but experienced programmer would make up for that by being able to use the algorithms in all proper 'best practice' ways one can think of. Whereas the graduate would just slam it in somewhere and call it a day even though there are now x more dependencies and whatnot, you get the picture.