I have always liked the opera browser, but one thing that has really sucked about it was the crappy file open/file save dialogs opera comes with. Picking around tonight, I ran across an option in opera's configuration that allows you to choose the file selector dialogs to use. It is cryptic as hell, but I found the commit page for the changes and got the needed information.
To make use of real kde4 open/save dialogs in opera, got to the config page by typing "opera:config" into the address bar, the scroll down to "File Selector", then change the setting to "2". The commit notes say:
0 - normal 1 - Qt 2 - GTK
For some reason, I couldn't get Qt to work, so I select "2" for GTK, and Bingo! I had usable dialogs in opera (you may need to restart opera). What a relief. If you use opera, it's worth a look.
While on the subject, you might want to check out the C00-14, Keramik and crystal_onyx_bull skins. Opera has come a long way in 10.0