Here's a great little trick to free up some device storage from xsrx over on the Modaco forums:
Something not mentioned, but that I assume is a good idea: clear your old cache first. Open Opera, click the little arrow in the bottom right, go to History, click the trash can and affirm that you want to delete all. If you don't do this first, you'll need to delete stuff from your old cache folder at Application Data\Opera9\cache. Now...
- Close Opera.
- 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.
- Open \Application Data\Opera\opera.ini in a text editor. [note: this directory was "opera9" not "opera" on my phone; "opera" is just help and skins]
- In the [User Prefs] section, add the following line: Cache Directory4=[full path to folder on storage card].
- Save and close opera.ini.
- Restart Opera. Your cache is now being written to your storage card.