Unless your computer is a throw-away, don't plug your 5V direct passthrough into one of its data ports. It can't support the current demand. Some computer USB ports will shut down if overloaded and provide a warning on-screen, others simply shut down the port, and still others don't do anything and just let the computer's motherboard burn up. As TomCatt said, use a powered USB hub at the least. Though, it's still sketchy since they are typically not designed to provide that much current either, but at least you won't potentially fry your computer or at best, burn up one of its data ports.
The best thing to use is a USB wall adapter with a minumum 2A output capability. Even then, you'll get a lot of voltage sag since the adapter will be heavily loaded. You'll probably be vaping somewhat under 5V, but you'll still be getting way more power to the atomizer than you would with a regular battery powered e-cig.
Even with a hub or computer data port, you'll get the limit of what the port can provide which is still probably more than you'd get with a standard battery-powered e-cig, but it stresses the port to the point of failure.
A good, but obscure way to go is to tap 5V directly off your desktop computer power supply by making a Molex to USB adapter. That's the white 4 pin one used on the old PATA hard drives. It's actually an obsolete connector, but most computer power supplies still have them. Probably not sojmething you'd be interested in doing, but desktop computer power supplies can output large currents. The current demand of an atomizer is insignificant for one. You would get the full 5V at the atomizer.