Writing a professional letter

When I was in school we had compulsory letter writing sessions both in English and Hindi.  The subjects were mundane but they the exercise emphasized that we should be careful about spelling, about salutations, about formatting...endless details that I, regretfully, forgot all about as soon as the exercise was over.  When I had to apply to graduate schools, I had to start all over again.
Now that I am a faculty, I receive many letters from students requesting for positions.  Most of the letters are written in poor English.  Many of them are addressed to Dear Sir.  Usually I respond back to these letters with a gentle reminder that not all teachers are males.  Sometimes the student will write back apologizing for his/her mistake.  I do not know whether the student learnt from the lesson though I would like to believe that he/she did.  But then I do like to live in an imaginary world.
My brother tells me that he too receives such letter.  And then today, I noticed this advice in the Science Magazine on How to Write e-mails when applying for graduate school.  It is worth reading as it provides many helpful pointers not only for undergraduate students but also for Ph.D. scholars about to apply for a post-doc position.