In certain areas, I've noticed people saying things like “La Suzanne” or “Le Guy”, referring to family members. How widespread is this? I realize it's nonstandard, but are there any rules that govern this use?
Je confirme ce que dit Steve Dispensa, c'est beaucoup plus utilisé dans l'est de la France que dans les autres régions. L'emploi dans l'est de la France est du langage courant encore actuel (et aussi employé par des personnes nées après 1945 +), bien qu'en voie de disparition, et n'a aucune connotation particulière. Employé ailleurs en France c'est connoté de façon péjorative.
I confirm what Steve Dispensa says, it is more widely spread in the east of France (and used by people born after 1945 +), than in other parts of the country. Usage in the east of France is declining but still vivid and used there it sounds just neutral. Used elsewhere it is indisputably more or less derogatory.
This is definitely a very rural usage, largely denoting "peasantry" (with its typical social stigma in modern society) and never heard in cities. Even in the countryside, I would say the usage is declining (along with most other dialectal practices) and mainly the prerogative of older people nowadays.
As for its origins: I'd be the first curious to know. My best guess would be an ironic jab at posh-sounding particle names...
It's something between the familiar level and the popular speak. I could use it with some people but will not with others, however relaxed I'm with them.
I can't resist to cite J. Brel (La Fanette) again. But it is difficult to deduce much from such a use in a song.
Nous étions deux amis et Fanette l'aimait
La plage est déserte et pleure sous juillet
Et le soir quelquefois
Quand les vagues s'arrêtent
J'entends comme une voix
J'entends... c'est la Fanette.
Be careful: in some areas, it might sound pejorative to use "le"/"la"/"les" before the name (or "ce"/"cette"/"ces").
I used it very recently in the chat. The goal was to ‘unpersonify’ someone who did something spectacular.
In this case, It had neither a pejorative connotation nor a “peasantry” one. It's just used to put emphasis on the fact that someone has a specificity. Specificities are often considered a bad thing, but it's not always the case.
However, I wouldn't have used that if we were not part of a family — a FL&U family I mean ;-).