As a point of reference, Gil is a reference to Jack Lemmon's character in Glengarry Glenross. He is the ultimate frazzled, over-the-hill salesman who can no longer cut it. Gil (in my opinion) seems to be out there to replace all the bit characters that Phil Hartman (RIP) played. Hell, in a very recent episode (was it the one with the "duff book of world records episode?), Gil is now even a lawyer (since there is no more Lionel Hutz for the Simpsons to use for legal advice).

Just to add to the list of tribulations that Gil has been subjected to - when Homer and Marge have their sex-in-public-places fetish, they destroy poor Gil's hotplate when they make a hasty escape from the police in the used-car lots hot-air balloon.