I'm not sure you really have to do both sides. When I had my left rear one done about a year ago, I asked the mechanic if the opposite side should be done too. He said no, if it's symptomless, then leave it; if it starts acting up, then do it. I thought that was pretty decent of the guy, he could have used it as a pretext to make more money off me, but he's not the type, and the money remained in my account instead of being transferred to his. Everything's been fine bearing-wise since.
It is a sizeable job, so I'd say take it to a reputable place, and let them do it in maybe half a day, whereas for the uninitiated it might take A LOT longer than that.