While browsing through the web and "in the search of the perfect file manager", i found one that comply my requirements quite well. The requirements are "tabbed browsing", lightweight and fast. I don't need any kind of skinning/theming or eye candy stuff. While reading a lot like 10 file managers for linux or 10 file managers for ubuntu and trying them out a lot, i'm stucked with pcmanfm. This file manager is fast, has tabs and also bookmarks. Yesterday a friend of mine found another one called qtfm.org. With qtfm, you can easily integrate scripts and use them via hot keys. It is smart two, so i just use pcmanfm "because i use it". But maybe qtfm has the benefit you are searching for.
Why no twin-panel filemanger? The answere is simple, two panels are not enough when i'm sorting files. I know i can use double commander but ... wellm you've already readed the because .