I've encountered several issues on different HP Elitebook Folio 9470m ultrabooks, after updating the BIOS to its latest version (F.46).

One series of ultrabooks with an Intel Hybrid HD (with SSD cache) suddenly stopped working with a BSOD and refused to startup. Reinstallation with the original DVD oddly failed as well, either during installation, or after installing drivers. We've worked around the issue by using a Microsoft (non-HP) DVD to install Windows 8, then download the latest drivers from the HP site.

Another ultrabook with an SSD had another problem altogether, but still related to the BIOS update. After the update, USB devices started to fail intermittently. Both the devices passed through the docking station the laptop was connected to, as well as devices plugged in directly in the laptop, stopped responding occasionally. A reinstallation of Windows did not resolve the issue. I've worked around that issue by downgrading the BIOS version to F.44, after which the USB issue no longer surfaced.

This shows that it's not always a good idea to be updating to the latest versions right away. I hope HP gets their act together and fix this.