I honestly believe people are overreacting to this whole situation. This won't be noticed by anyone, but I might as well put my predictions out there...
The acquisition will, undoubtedly, assist Oculus in bringing CV1 to the market in an even better form than it would be without. $2 billion is not pocket change, and they now have the financial backing to dictate to hardware manufacturers that will create the products they desire.
People will see little to no effect of the Facebook acquisition until the launch of CV1 and most likely a little after where Facebook will eventually bring out a social, Second-Life-like, PlayStation Home-like, VR MMO to the market. I believe this is where Facebook sees their profit opportunity in Oculus. Facebook does not care directly about the hardware, nor do they care about people using it for gaming. What Facebook has acquired this for is so they can create a social VR MMO - something that I've seen many people ask for, albeit from a gaming company and not Facebook. 
And yes, this will have advertisements on it. Not very obtrusively like some of you seem to be speculating, but imagine VR billboards as you walk down a street or watching a video in VR will have an advertisement before it (no different than YouTube). Facebook will also expand this VR MMO to include their more casual gaming line - so imagine this MMO will now have Farmville integrated. 
I do not disagree that this sounds terrible, but my prediction is that this will remain its own separate entity and, guess what! If you don't want to play Facebook's shitty VR MMO, you don't have to play Facebook's shitty VR MMO! 
In terms of the gaming-sphere, Facebook won't touch it. Oculus will continue to operate independently as it has before to bring good gaming VR to the market.
Moving into future versions of the Rift (CV2, CV3...), the acquisition will have minimal affect beyond providing Oculus with more resources to improve the quality of their product. You might see one or two useless features in there for the purpose of Facebook's MMO, but usage of these features will be up to developers to integrate them, so they'll likely be ignored for the hardcore gaming population.
TL;DR: All in all, I'm not happy about the acquisition, but I believe that people are vastly overreacting. I will withhold judgement until I see something concrete that sways me one way or another. My predictions are that this will vastly assist Oculus in bringing a better platform to the market, quicker, with no interruption to their original vision. In the future, Facebook will utilize their new hardware to bring a social VR MMO to the market where they'll bombard you with ads, but this will not negatively affect the Rift as you don't have to play their game.