This little guy has been visiting me at work almost every day for the last few weeks. He lives across the street and he comes running as soon as I pull up in the morning.
As much as I agree, trying to keep indoor, a cat that's used to life outside, it's really hard, and may stress them out a lot.
Several years ago at my (then) house, we had a regular visitor that I called Neighbor. There was one winter in particular that was especially cold, so when he came to visit, I tried bringing him in to help him warm up, and he practically fought and cried the whole time. Of course after a few minutes of getting toasty, I let him go on about his routine.
I imagine doing that for an extended period of time would greatly stress the cat out in an unhealthy way.