Yes, essentially I follow the same simple system. But to avoid adding each bin directory to the path, I create for each application an executable script in /us

Yes, essentially I follow the same simple system. But to avoid adding each bin directory to the path, I create for each application an executable script in /usr/local/bin that performs an "exec /opt/package/bin/app-name $@". The only directory to add to the path is /usr/local/bin. Then, as you say, managing multiple application versions is as easy as repointing the symlink in /opt. No need for package managers that do who knows what to your system. The one exception is for shared libraries, which I build to /usr/local. That way 'make' can find them easily without fiddling with LDPATH.