I've only been brewing for a month (just did my third batch last night) and have ONLY used induction to do this.
Yes, all the reports are true... to go from "room temperature" to boiling takes about an hour and a half (I wrap my brew kettle with a makeshift blanket and leave the lid on for a good portion of it to keep in heat), but it eventually boils and can keep it there with the heat at about 50%
I use one of these:
As SankePankey indicates, the CookTek line is (in my mind) the Rolls Royce of cooktops (though much better in terms of reliability than a RR). I have one of their other units and probably will for the rest of my life. Apart from brewing, I also cook a lot of complicated meals and the control I have with the CookTek is amazing.
As for the temperature modes, I wouldn't rely on those too much. Both of my cooktops have a temperature setting, but since it's being monitored through the ceramic top, it has a pretty wide "swing".
Not sure if you could do a thermostat connection without some hacking. Mine (I have 3 different models) all get powered up in "standby" mode so anything that shuts off the power would need human intervention to resume.
That being said...
There are benefits over gas apart from efficiency, blah blah. For one thing, I can leave a towel near/on the "burner" without a hassle. The handles don't really heat up (apart from the pot itself heating it up), and I can do this in a closed garage which is handy since some neighbor kids with REALLY POOR "boundaries" won't come wandering over and, oh, CLOSE MY GARAGE DOOR ON ME. (Yes, they've done it. It's kinda like Lord of the Flies.)
Where was I... Oh yes... No tanks to refill, etc.
The 220v models are tempting idea since I have a spare 220v circuit where a gas clothes dryer would be. (I prefer to think of it as a "dedicated brewing circuit".) Maybe someday after I fix a hundred other things which are more pressing.
I'll probably go with gas at some point but, until then, my little Iwatani is doing the job... if a little slowly...
"Wait, I can make this stuff myself? Why didn't I do this sooner?" - Me