This question already has an answer here:
My wife and I share the same PC, we only use two different users for easier switching between each other's task without interrupting anything. We're not concerned about privacy nor security.
Whatever solution you think you know, I've already tried, nothing that could work on Ubuntu versions up to 12.10, doesn't work anymore on 13.04, that's why I'm asking something that seems to be answered so many times in the past.
I've already disabled the "lock screen" for both users, and this is not enough.
Please tell me what could be a good solution for this. Thanks!