Thanks. I will add this to the help the next time I update it -- I'll probably add a page about this permission stuff.
But it is really a problem with your particular computer -- some program you installed changed the permissions incorrectly. This is usually because of a bug in the program's installer, but it could be an indication that your system has been compromised.
Note: this is not something that Tunnelblick has anything to do with except that Tunnelblick notices the problem and complains about it -- in other words, Tunnelblick is just the messenger. Such problems are fairly rare. The systems that I have updated to 10.9.3 do not have this problem -- the ownership/permissions on /Users was root:wheel 0755 before and after the 10.9.3 update.
kextstat | grep -v com.apple
ls -l /Library/LaunchDaemonsls -l /Library/LaunchAgentsls -l ~/Library/LaunchDaemons
kextstat | grep -v com.apple
ls -l /Library/LaunchDaemonsls -l /Library/LaunchAgents
ls -l ~/Library/LaunchAgents
sudo chmod 0755 /Users
sudo chflags nohidden /Users
Setting the correct permissions demanded by Tunnelblick
sudo chmod 755 /Users/
ls -la should look like this
drwxr-xr-x 6 root wheel 204 23 Okt 2013 Users
This will be reset by reboot and has to be done once, e.g. as a startup script, before starting Tunnelblick