I said yes, and I would use it, but it doesn't need to be
that complex. I think that
Giant In the Playground Games is a good place to start. It still makes you roleplay ("what do you say? What's the deal you're offering?"), and it gives you rules to follow for mechanical resolution, while also giving you a sliding scale (1-4 means he's open to the idea, but not quite there, and may even counteroffer).
My negotiation rules are modeled on this, but still pretty different (adding a "+∞ Impossible:" level to Risk vs Reward, with skills like Intimidate able to lower that down, etc.). Also, Bluff to deceive is more along the lines of "does he believe me" (with appropriate modifiers for outlandish or very believable deceptions), instead of "does he do what I want him to do?" For example, instead of a "Bluff the guard to get into the castle" situation, you have a "Bluff the guard to make him think we're diplomats on the run from pursuers, and now see how he reacts to our deception" situation.
I think this sort of thing still allows for a lot of meaningful social RP play, while also giving you the tools to determine success or failure mechanically. Mechanically, you get "I failed my negotiation check by 7... he just isn't willing to go along with that. I need to come up with something new. Time to RP that back and forth, then roll on another proposal." This (along with Bluff per deception to convince them you're not lying, not to make them react a certain way) makes things a lot more roll-intensive in social encounters, rather than binary, which is something I like.
Both the PC's mechanical skill and the player's personal interaction become important to resolving the scenario, and it's more versatile, flexible, and dynamic than "I rolled Diplomacy to befriend him, and he likes me now" or "I use Bluff to make him let us inside, telling him we're diplomats".