However an OEM copy cannot be transferred to a new motherboard without calling Microsoft and begging for mercy.
You don't really need to beg for mercy. Just tell them it will only be installed on one system when asked, and if they as why, tell them you replaced your motherboard.
I reactivate OEM copies on a bi weekly basis and if what I'm doing isn't strictly EULA kosher, none of the phone techs seem to give a shit.
I have one OEM copy of windows XP that's been activated on at least thirty different systems (usually one at a time).
A typical phone activation:
Woman speaking English in a heavy Indian accent: Hello, my name is Banu. What MS Product can I help you activate today?
Me: Windows Server 2008 R2 Enterprise.
Miss Banu: May I have the first six digits of your activation code?
Me: 123456 (or whatever)
Miss Banu: And why will you be reactivating?
Me: Just installed a new motherboard.
Miss Banu: And how many computers wi..
Me: Just this one.
Miss Banu: Ok. I will now read the digits for box A....
*6,000 years and more digits than Pi later*
Miss Banu: Now click next and you should be activated.
Me: Ok, it worked. Than...
Banu (interupting in haste): Thank you for calling Microsoft! Goodbye! *click*