I have been following induction brewing for a while. At one point, where I lived I could only do electric (I now have a big gas stove, but I do have to compete for the kitchen space still). So I will share what I know..
Induction boil times and boil capacity is determined by the wattage of the Induction plate. Just like gas is for BTU, or resistive-electric (traditional) stoves and wattage. Wattage for induction electric does not equate to wattage for resistive electric stoves, either.
The highest power anything you can plug into a kitchen 20A 120V circuit is 2000W. 2000w portable induction plates are very rare in the USA. (They're more common in countries where energy prices are higher, which forces people to buy energy efficient appliances).
There are also premium induction stoves or built-ins for the kitchen, which use 240V. Expect to pay an extra $1000 for such a stove. However it may be worth it if you value the conservation value or faster boil times. (If you don't, it will take a long time to pay for itself in energy savings, but eventually it will...).
It looks like you can find 2000W portable induction plates for $200-$400. Pricey, but they are not things you can find at Target or Walmart. Using a smaller induction plate like 1300W will get you results like some have posted here. I would love to hear from someone who uses a 2000W portable or a built-in model....
The other option for electric brewing is a DIY brewing rig, using 120V heating elements, or 2 120V heating elements (on separate 120V circuits!), or 240V electric if you are so lucky to have that option.
Here is a nice build of a single-120V element brewing system, from Brew Your Own magazine:
I have been considering building this with 2 120V elements (just unplugging one once the roiling boil kicks in).