I am back to full steam, this is what fixed my problem:
Symptoms: “Still waiting for root device” – NO sign; saveboot works (holding right shift on boot)
Solution:
After trying everything,
Disk utility (on safeboot, on install disk, on another mac)
DiskWarrior (on safeboot, on bootdvd, on anothert mac)
fsck (even advanced options)
pram reset
smc reset
etc. in all possible configuration, by even removing the disk from the unibody case and attaching it via USB to another mac.
I finally found a solution. These failures are always due to faulty BIOS settings or faulty kexts on OSX86. But since I am on a MacbookPRO, there is no BIOS.
Long speech short
Replace IOStorageFamily.kext in /System/Library/Extensions with one from a working mac, or from the installation disc using Pacifist, or whichever way you prefere.
Fix permissions and ownership, repair permissions with discutility. Remove caches.
And you are good to go.
I can imagine that sometimes other kexts may be the faulty ones. In such cases it is always good to analize verbose mode first.
This is how I managed to fix my problem without having to reinstall.