So, like most people picking up a modern set of rules, I ran into the Joker use restrictions rules. I did some research and came up with some interesting links that others may find useful.
The first one is for the Sabra rules, which apparently were penned by the game's author (according to the copyright note on the page):
These Sabra rules make the game tougher, but I like that they are pretty clear. I am planning to use them for my future plays.
Also, here is an interesting overview of the rules that comments on the variants around Joker use and also describes three sets of game rules:
Lots of good stuff on that page.
Finally, here's another site covering rule variations:
If nothing else, I hope this provides a better perspective on the rule variations.