Today, I ended up in a site showing famous people faces in a very first plane. I just got impressed by the quality those photos had.
What do you think are the factors you have to tweak to reach that quality?
In this case, I think they've used a high quality prime lens with a very big aperture. The camera body must be also a important factor. But is there anything else?
What about the lighting in those photos?
Well, the lighting in the photos look like lights on the background, and two relatively large lights illuminating their face (you can see the catchlight in the eyes), very possibly some rim light too.
You're spot on about the large aperture, even the ears are out of focus. However, considering how sharp the photos are, its possibly stopped down a bit (but not much at all) and the lens is close to the subject to decrease depth of field. Since he's shooting 8x10 view camera, I imagine the depth of field can be pretty shallow when needed.
As far as camera goes, who knows. But you can get amazing results in a portrait studio setting because of the lighting with many, many cameras these days. Given that he's shooting that many celebs though, I would imagine he could be using something like a medium format hasselblad - but frankly who knows.
Besides all that...check out this strobist post for a behind the scenes look at this photography.
EDIT: That specific video shows the two large boxes like I said, as well as a beauty dish center and up. It looks like he's shooting with a 8x10 view camera.
The lighting appears to be a single large roundish softbox (like the Elinchrom Octa) immediately behind the photographer/camera in most of the images. The shadow pattern is very similar to what you'd get with a ring light -- the outlines are darker than the center and there are no obvious shadows under the eyes or nose, etc. -- but softer. There is a vertical stripe "missing" from the lighting pattern, though -- and that'd be the photographer's position. The stripe is rather rectangular, though, which leads me to believe that the photographer has placed a gobo either behind -- or perhaps in front of -- the camera in order to keep the reflection out of the subjects's eyes. At least one picture, though (Paris Hilton) seems to have used a similar setup with either a large square softbox (Quadra, if we're actually in Elinchrom country) or two vertically-oriented rectangular softboxes (still huge) placed either side of the camera.
The camera is definitely a view camera, very likely an 8x10 with a 210mm lens going by the perspective -- which makes these photographs essentially macro photos. The aperture setting could actually be quite small by 35m-format standards -- f/22 or smaller wouldn't be out of the question for the depth of field we're seeing.
Also, do not forget post editing. Slight sharpening, careful highpass filtering, to highlight all skin details.