My company currently has no policy against it. Rather than ask and make them think about how to "handle" e-cigs, though, I just stealth-vape at my desk. My boss' cubicle is immediately next to mine, and he's seen my PV sitting on my desk and talked to me about vaping (when he first saw a battery hanging off my USB port charging), but he has no idea I use it while at work. The guy who used to occupy the cubicle on the other side left the company, and I recently had a drink with him. I pulled out my e-cig and started puffing away, and he asked me if I did it at work. He said he had never noticed.
I stealth-vape because I'm not sure if it would be approved, not because I know it's against the rules. If the company had a policy, I would abide by it.