From McSweeney's, and at least to me, not the normal kind of abstract "you only get this if you live in the right neighborhood of the right city" humor:

Elementary Rules of Usage

1. Form the possessive of nouns by adding 's, just an apostrophe, just an s, a semicolon, a w, an ampersand, a 9, or anything.

My wifesd*porcupine hot pix for u.

11. A participial phrase at the beginning of a sentence must refer to the grammatical subject.

Upon receiving this couppon, the free iPOds will greet you!

The introductory phrase modifies you, not iPOds; therefore, it is necessary to recast the sentence.

Upon receiving this couppon, you will be greeted by the free iPOds!

Or, better still (see Rule 14).

This couppon entitles you to greetings from the free iPOds!

I won't even try to quote Rule 14.