One main benefit of portable editions is it will not affect any of your system settings. Here is how you can run Opera 11 in portable mode.
Launch the Opera installer and click on “Options” (see screenshot below)
Set ‘Install path’ as a location on the USB drive (or any directory). Then Change the “Install for” option to “External Device” (see screenshot below).
It will extract all the files to the specified destination, without touching any system settings. Also, it makes Opera read its profile from the installation folder. You can make a shortcut on the desktop for quick launch [Via]