Opera uses a very flexible profile system to configure user settings and preferences. When you install Opera, it asks you whether you want to install for individual users or not; this defines where Opera stores its settings. It is normally better to allow Opera to create individual profiles, as you can then set up additional custom profiles easily. The big advantage is that you can run different Opera profiles at the same time, giving great flexibility in how you can set Opera up. See EditingINIFiles for more general information on INI files.
When using individual users profiles, to find the directory where your data is stored, open Help » About Opera and see where the Preferences path points to, for example in Windows XP it is usually C:\Documents and Settings\userX\Application Data\Opera\Opera\profile\opera6.ini
(From now on to make the page clearer I will shorten C:\Documents and Settings\userX\Application Data\ to APPDATA — thus our profile directory is now written APPDATA\Opera\Opera\profile\opera6.ini)
With this knowledge it is very easy to manipulate the profiles to your pleasing. As an example, lets say you have a profile you've used for a while and you want to make a new clean profile without any of your customisations; here are the steps to creating a clean profile which you can then easily run simultaneously with your normal profile. We will assume the install pattern above, but you need to change the paths shown below depending on your install and profile paths!:
Opera Directory=C:\Documents and Settings\userX\Application Data\Opera\Opera\profile
Opera Directory=C:\Documents and Settings\userX\Application Data\Opera\OperaNew\profile
Now clicking on our old shortcut loads Opera with the old profile, and clicking the new shortcut makes Opera start with the clean profile. You can run both of them at the same time, just like having two different installs of Opera running, but without having to install twice! As many profiles as you want can be created, and can be placed anywhere you like.