Like the gears, but don't like device icons at all.
Haikarainen version is beautiful, but does not resemble the concept of SIMPLE and FAST. And at first look, the impression is that we're talking about a complete engine, not a SIMPLE (!) library.
Another minus is that device icons aren't original. It's a drawback, as for me, and the first time I went on SFML website, I instantly noticed that icons are "stolen", even if they are in public domain. This kind of "theft" is ok when someone is customizing his desktop with a icon theme, but it's not acceptable for a logo, in my opinion, which has to resemble the project it represents.
Look at Qt toolkit. It is by far more complex and provides a huge functionality, think how many icons could they put in their logo... But they've chosen a simple green icon, and it is clear as the library itself. And if miniaturized, it still looks nice.
Like a lot Cuban-Pete, Brendon, jmglez and Cpl.Bator styles, as for me, they have to work a little more on their ideas...