What you see is perfectly normal not just for Snow Leopard, but for all versions of OS X. Only if you were using a non-standard setup of OS X before would you be able to dig around in other user's stuff.
Also, you shouldn't use the Get Info window to try to change ownership or permissions on something about a user account. The fact that you can do it doesn't mean it makes sense in normal circumstances. Sooner or later, you or another admin user will need to repair permissions for the startup disk and that will revert everything back to normal.
The best way to share documents in any UNIX environment (OS X is UNIX) is to honor the security of separate accounts and use the Shared account (at /Users /Shared) for sharing documents. Any user can add to and take from the Shared folder. That's what it's for.
You can also create a disk partition ("drive volume") for sharing. OS X allows setting any non-startup internal disk as "Ignore ownership on this volume." The partition will be like any Windows drive volume, open to anything and everything. Don't store any password or financial data on it since it has not much network security.
Each user account has its own separate area. If that isn't what you want, simply delete all the other user accounts and give your password to all the other users. Then you can keep all your documents in one account area.... but it will just end up a mess like the "Documents and Settings" area of many Windows computers.