For those Opera fans running Ubuntu on 64-bit AMD cpus:
Opera only provides Ubuntu Linux packages for i386, but there is a way for forcing the installation of the provided i386 package by borrowing a shared library it depends on (Qt) from an i386 Ubuntu package:
1) Download the Ubuntu version of Opera 9 for i386 Linux from the official site.
2) Download the libqt3-mt deb package file for i386. (Try using the search interface if link is broken)
3) Create a temp dir for libqt3-mt contents:
$ mkdir qttempdir
4) Unpack the libqt3-mt deb package with
$ dpkg-deb -x libqt3-mt_3.3.8really3.3.7-0ubuntu5.2_i386.deb qttempdir
5) Copy the i386 shared Qt lib to your /lib32 dir (removing minor version numbers from the filename, or creating symlinks):
$ sudo cp qttempdir/usr/lib/libqt-mt.so.3.3.7 /lib32/libqt-mt.so.3
6) Force the Opera debian package installation with
$ sudo dpkg -i --force-all opera*.deb
