I've heard quite a long ago about an architecture called Itanium, I also have heard that it is considered good but what I haven't heard of it yet is why people are not using it if it is as good as it says it is ?

now from what I know, the Itanium is about the only 64-bit platform, the others are fakes.

could anyone comment on that ?

The Itantium and the Itantium 2 just sucks for workstation use and some server environments. That is how the computer industry puts it. A few months ago Intel just stated that is not good for workstation use. The Itantium processors are great to crunch numbers but the code have to be 64-bit or else a huge performance penalty.

What are you comparing? Intel's processors? AMD has real 64-bit processors called Opteron, Athlon 64, and Athlon FX. These processors can run 64-bit and as well as 32-bit code. Also like AMD's previous processor lines, it does not have any penalty if it is running 32-bit code. These processors are much cheaper than Intel's processors.

how do Opteron, Athlon 64, and Athlon FX compare versus Itaniums in 64-bit mode ?

Opteron, Athlon 64, and Athlon FX do very, very well in 64-bit. They are a lot better for servers and also in some engineering programs. Though not a lot programs are programmed using 64-bit code.