Using my OEM windows license in a virtual box image?

I've stumbled across this question and was curious about Windows 7 Professional (my case).

I think EULA (to be found here) answers this conclusively. Below see relevant parts (most notably 3/d).

1. OVERVIEW.

    b. License Model. The software is licensed on a per copy per computer basis. A computer is a
    physical hardware system with an internal storage device capable of running the software. A
    hardware partition or blade is considered to be a separate computer.

2. INSTALLATION AND USE RIGHTS.

    a. One Copy per Computer. The software license is permanently assigned to the computer with
    which the software is distributed. That computer is the “licensed computer.”

3. ADDITIONAL LICENSING REQUIREMENTS AND/ OR USE RIGHTS.

    d. Use with Virtualization Technologies. Instead of using the software directly on the licensed
    computer, you may install and use the software within only one virtual (or otherwise emulated)
    hardware system on the licensed computer. When used in a virtualized environment, content
    protected by digital rights management technology, BitLocker or any full volume disk drive
    encryption technology may not be as secure as protected content not in a virtualized
    environment. You should comply with all domestic and international laws that apply to such
    protected content.

I am not a lawyer, but as long as you don't activate multiple copies of Windows (whether physical or virtual) using the same key, it should be fine.

Check out the Windows 8 Pro OEM EULA for example:

Under Additional Terms / License Rights and Multi User Scenarios it states:

So you should be able to wipe Windows, reinstall inside a VM and activate using your key. Remember however that with Windows 8 PCs there is no COA sticker any more, and the key is embedded in the BIOS instead and automatically picked up by the installer.