Seriously though I dont think many people are actually locked up for use nowadays. Im willing to be corrected but I haven't, in my experience, seen it much.
As mentioned below I believe personal possession laws should be refactored towards education, support and therapy (if desired)
Here where I live, in Brazil, you will get a lot of hassle if you're caught for marijuana possession. If you're black or poor, you're probably going to get a lot more hassle (being beaten up and being locked up for some time are almost certain to happen).
Generally, you can get away with 10 grams or something like that, but not without hassle. You better pray to Jah to not get caught :)