Here's my feedback - hope it's still useful :)

1. currently flash doesn't work on my system (x86 stable 32bit) with
   opera.

   last version that worked:
   opera-11.01.1190
   adobe-flash 10.2.159.1

   when the following packages became stable, flash stopped working in
   opera:
   (IIRC, both were upgraded at the same time in my system)

   opera-11.11.2109
   adobe-flash 10.3.181.26

   later, opera-11.50.1074 was stabilized, but flash still doesn't work.

   with firefox, flash works flawlessy. current version installed:
   firefox-bin 3.6.17

2. I've been unable to make it work.

3. adobe-flash 10.3.181.26 (-kde -vpau)
   It should be the 32bit version - my system is 32bit...

   opera plugin path: /usr/lib/opera/plugins:/usr/lib/nsbrowser/plugins

   $ ldd /usr/lib/nsbrowser/plugins/libflashplayer.so
   linux-gate.so.1 =>  (0xffffe000)
   libX11.so.6 => /usr/lib/libX11.so.6 (0xb6b26000)
   libXext.so.6 => /usr/lib/libXext.so.6 (0xb6b17000)
   libXt.so.6 => /usr/lib/libXt.so.6 (0xb6ac7000)
   libfreetype.so.6 => /usr/lib/libfreetype.so.6 (0xb6a44000)
   libfontconfig.so.1 => /usr/lib/libfontconfig.so.1 (0xb6a15000)
   libpthread.so.0 => /lib/libpthread.so.0 (0xb69fc000)
   librt.so.1 => /lib/librt.so.1 (0xb69f3000)
   libgtk-x11-2.0.so.0 => /usr/lib/libgtk-x11-2.0.so.0 (0xb6656000)
   libgdk-x11-2.0.so.0 => /usr/lib/libgdk-x11-2.0.so.0 (0xb65c2000)
   libatk-1.0.so.0 => /usr/lib/libatk-1.0.so.0 (0xb65a7000)
   libpangoft2-1.0.so.0 => /usr/lib/libpangoft2-1.0.so.0 (0xb6581000)
   libgdk_pixbuf-2.0.so.0 => /usr/lib/libgdk_pixbuf-2.0.so.0 (0xb6567000)
   libpangocairo-1.0.so.0 => /usr/lib/libpangocairo-1.0.so.0 (0xb655b000)
   libcairo.so.2 => /usr/lib/libcairo.so.2 (0xb645d000)
   libpango-1.0.so.0 => /usr/lib/libpango-1.0.so.0 (0xb641d000)
   libgobject-2.0.so.0 => /usr/lib/libgobject-2.0.so.0 (0xb63dc000)
   libgmodule-2.0.so.0 => /usr/lib/libgmodule-2.0.so.0 (0xb63d7000)
   libglib-2.0.so.0 => /usr/lib/libglib-2.0.so.0 (0xb62df000)
   libssl3.so => /usr/lib/libssl3.so (0xb62af000)
   libsmime3.so => /usr/lib/libsmime3.so (0xb628b000)
   libnss3.so => /usr/lib/libnss3.so (0xb6185000)
   libnssutil3.so => /usr/lib/libnssutil3.so (0xb616d000)
   libplds4.so => /usr/lib/libplds4.so (0xb6169000)
   libplc4.so => /usr/lib/libplc4.so (0xb6164000)
   libnspr4.so => /usr/lib/libnspr4.so (0xb6131000)
   libdl.so.2 => /lib/libdl.so.2 (0xb612d000)
   libm.so.6 => /lib/libm.so.6 (0xb6108000)
   libc.so.6 => /lib/libc.so.6 (0xb5f8d000)
   /lib/ld-linux.so.2 (0xb787a000)
   libxcb.so.1 => /usr/lib/libxcb.so.1 (0xb5f72000)
   libSM.so.6 => /usr/lib/libSM.so.6 (0xb5f69000)
   libICE.so.6 => /usr/lib/libICE.so.6 (0xb5f51000)
   libz.so.1 => /lib/libz.so.1 (0xb5f3c000)
   libexpat.so.1 => /usr/lib/libexpat.so.1 (0xb5f16000)
   libXfixes.so.3 => /usr/lib/libXfixes.so.3 (0xb5f10000)
   libgio-2.0.so.0 => /usr/lib/libgio-2.0.so.0 (0xb5e20000)
   libXi.so.6 => /usr/lib/libXi.so.6 (0xb5e12000)
   libXrandr.so.2 => /usr/lib/libXrandr.so.2 (0xb5e0a000)
   libXcursor.so.1 => /usr/lib/libXcursor.so.1 (0xb5dff000)
   libXrender.so.1 => /usr/lib/libXrender.so.1 (0xb5df5000)
   libXcomposite.so.1 => /usr/lib/libXcomposite.so.1 (0xb5df1000)
   libXdamage.so.1 => /usr/lib/libXdamage.so.1 (0xb5ded000)
   libresolv.so.2 => /lib/libresolv.so.2 (0xb5dd6000)
   libgthread-2.0.so.0 => /usr/lib/libgthread-2.0.so.0 (0xb5dd0000)
   libpixman-1.so.0 => /usr/lib/libpixman-1.so.0 (0xb5d60000)
   libEGL.so.1 => /usr/lib/libEGL.so.1 (0xb5d51000)
   libpng14.so.14 => /usr/lib/libpng14.so.14 (0xb5d2d000)
   libQtGui.so.4 => /usr/lib/qt4/libQtGui.so.4 (0xb52e2000)
   libQtCore.so.4 => /usr/lib/qt4/libQtCore.so.4 (0xb5056000)
   libxcb-shm.so.0 => /usr/lib/libxcb-shm.so.0 (0xb5052000)
   libxcb-render.so.0 => /usr/lib/libxcb-render.so.0 (0xb5049000)
   libGL.so.1 => //usr/lib/opengl/xorg-x11/lib/libGL.so.1 (0xb4ff1000)
   libgcc_s.so.1 => /usr/lib/gcc/i686-pc-linux-gnu/4.4.5/libgcc_s.so.1\
    (0xb4fd5000)
   libXau.so.6 => /usr/lib/libXau.so.6 (0xb4fd0000)
   libXdmcp.so.6 => /usr/lib/libXdmcp.so.6 (0xb4fca000)
   libuuid.so.1 => /lib/libuuid.so.1 (0xb4fc5000)
   libstdc++.so.6 => /usr/lib/gcc/i686-pc-linux-gnu/4.4.5/\
    libstdc++.so.6 (0xb4ed9000)
   libXxf86vm.so.1 => /usr/lib/libXxf86vm.so.1 (0xb4ed2000)
   libX11-xcb.so.1 => /usr/lib/libX11-xcb.so.1 (0xb4ecf000)
   libxcb-glx.so.0 => /usr/lib/libxcb-glx.so.0 (0xb4ebc000)
   libdrm.so.2 => /usr/lib/libdrm.so.2 (0xb4eb1000)

4. 32bit

5. XFCE 4.8 - compositing off

6. $ opera --full-version

   Opera 11.50 Build 1074 for Linux i386.
   OS: Linux 2.6.37-gentoo-r4
   Architecture: i686
   Compositor active: No
   Toolkit: Gtk 2.24.4 using MurrinaGraphiteGentle
   Desktop environment: Xfce
   Window manager: Xfwm4
   Screens:
   0: 1024x768 depth 24,32 (default)

7. $ lspci | grep -i vga
   01:00.0 VGA compatible controller: \
   ATI Technologies Inc RV280 [Radeon 9200 SE] (rev 01)

8. $ grep -i -e "loading.*drivers" -e unload /var/log/Xorg.0.log
   [40.327] (II) Loading /usr/lib/xorg/modules/drivers/radeon_drv.so

   $ equery belongs /usr/lib/xorg/modules/drivers/radeon_drv.so
   x11-drivers/xf86-video-ati-6.14.1 \
   (/usr/lib/xorg/modules/drivers/radeon_drv.so)