I've had very few concerns about this ever since they said that a separate Bioware studio was working exclusively on the multiplayer. So long as it's not detracting from the single player, I'm happy.
Still, I'm not 100% clear how this "Galaxy at War" system will interact with multiple Shepard career files. Will gaining points "improve" the chances of total victory across all saves, or will it unlock a pool of--for want of a better term--"points" that you can access and choose whether or not to "spend" in any given career? I'm hoping for something like the later as (especially for my main Shep) I want my first playthrough to be "pure" without MP influencing events. And then there's my loserShep for whom I fully intend to make things as difficult as possible,
Obviously just holding off on MP until after my first playthrough would avoid any unwanted interactions, but I'd just as soon have the option.