It isn't acceptable, no. I tried Duck Search (aka Bing) for a couple weeks and in the beginning I wouldn't know that I wasn't getting the results I was looking for and eventually realized that the results just sucked compared to Google.

I found myself having to second guess the results and then did a Duck / Google hybrid for a while, going to Google when I didn't get what I was looking for and eventually it was too much friction. I equate it with when I used to use two different text editors, one for speed (Sublime) and another (IntelliJ)for step-debugging because Sublime didn't have that part well implemented and it was just maddening to have to switch back and forth all the time and learn/maintain two sets of keyboard shortcuts etc.