Using GSFinder+ 'Open>Choose program..." feature under "\Windows\Opera9\opera.ini" edit with a text editor or built in Word Mobile (pick doc from the Choose Program list).
Change the "Maximum Allowed Tabs=3" line to a higher number (I've doubled mine to 6).
Save, exit Word Mobile, load opera and try opening more than 3 tabs,
Haven't come across any issues doing this although it may have been limited to 3 to ensure memory wasn't used up as I've had a few memory warnings about that when opening lots of complicate pages.
If you're into reading your RSS feeds from Google Reader theres an iPhone version that runs well from Opera on the Diamond, open all your articles in new tabs makes things really easy (especially with the Max tabs limit removed)