The only ready-made folders that could be used for that are /tmp and /var/tmp. /tmp may be cleared on each reboot, and /var/tmp may be removed after some period of time such as one week. In any case, they are for temporary files. Even if Ubuntu 12.04 doesn't touch /var/tmp, you never know what the next version is going to do, so you should always assume that the contents of these directories are liable to be removed without warning.
If the fact that these are temporary is a problem, you need another solution. If I want other local users to have read access to my files, I set my home directory's mode to 755 (this is what I usually do); but in that case I take care that any secret files or directories within my home directory are set to 600 or 700 respectively.
The combination of temporary files + home-directory-readable-by-all usually suffices. If you really want a shared folder, you need to create, for example, /home/shared, and set it to 777 or to 1777 (the 1777 means writeable by all like 777, but only the owner of a file may remove the file). More advanced setups include setting the directory setgid bit and playing with user groups, but I'm not elaborating on this.
I generally don't like the 711 mode for directories; I find it confusing and it's not clear how secure it is (I like to assume that readable means readable, even if you have to guess its name to access it).
In conclusion, the solution depends on what you are trying to do.