In Mountain Lion how do I set, in one place, the PATH environment variable for all newly launched applications? On Ask Different there are many questions regarding the PATH environment variable and how to set it for applications launched by a shell, by spotlight or via the finder (typical questions: How to set PATH for Finder-launched applications or How to change PATH environment variable...).

Answers range from sh startup scripts to /etc/paths to /etc/launchd.conf. Here I am after the answer for a unified setting of PATH for all apps under Mac OS X Mountain Lion 10.8.2.
After many trials with different options I conclude:

Is there a unified way to set the PATH for applications launched by different means (like shell script, Finder and Spotlight)? Well, yes and no:


No: Setting PATH in shell start up scripts (e.g. .bashrc) works only for apps launched by shells.
No: Setting PATH for the current launchd process via launchctl setenv PATH &lt;...&gt; does not work for me at all.
Yes: Setting PATH in /etc/launchd.conf (and restarting the system) will make the appropriate PATH visible in  applications launched by Spotlight, Dock and Finder and subsequently (local) shells. 
No: Remotely invoked shells do not inherit the environment. (See ...why do remote shells via ssh do NOT inherit the environment..) 


Notes for set-up of shells:


For correct functioning in local shells it is important to switch off the use of /usr/libexec/path_helper, because the default paths in /etc/paths might change the order of the paths in PATH.**
To accommodate remote shells you need to re-import the launchd environment into the shell. Use something like this in your .bashrc:


# the vexatious path stuff
eval $(launchctl export)


Unfortunate consequences of the whole issue are:


No way to have these unified settings on a per user basis. (~/.launchd.conf does not work.)
No easy way to construct the PATH from different sources using techniques like home directory expansion et al.