Birds have the flu and Tigers lose their Bluetooth

For some weeks now, MacBidouille's forums have been flooded with reports of Bluetooth shutting down for no known reason on OSX Tiger (at leat since 10.4.3 update). As my computer became affected by the same problem, I tried but failed to find a way out of it.
On different models (Powerbook - 12" 1.33 GHz in my case, 15" 1 GHz in another, from a Powermac to an iMac G5), the Blutooth icon disappears from the menu bar, but also from the System Preferences, as if it had bever been there! System Informations simply states: "Bluetooth: not available". Even more puzzling, this epidemy affects external modules (USB) as well as the internal ones.
We are now collecting information about that mysterious phenomenon which - it seems - so far got no answers in Apple forums, and might not even be officially acknowledged by Cuppertino. Beyond getting a technical diagnosis, what we need is a simple way to restore Bluetooth functionalities without going through a Windows-style reinstall of the system...