As is always the case, Cache for web browsers can quickly eat up memory. After some research, I found how to move the Opera cache to another location.

Note: I updated these instructions as the \Application Data folder has two Opera folders (Opera and Opera9). The opera.ini is in Opera9

Also, I would suggest clearing your cache before moving to ensure all the old cache files get deleted.

1. Close Opera.
2. Create a folder on your storage card where the cache files will go.* I chose \Storage Card\Program Files\Opera\cache4, but I don't think the folder structure or folder name matter.
3. Open \Application Data\Opera9\opera.ini in a text editor.
4. In the [User Prefs] section, add the following line: Cache Directory4=[full path to folder on storage card].
5. Save and close opera.ini.
6. Restart Opera. Your cache is now being written to your storage card."

pw-man