Sam has a good point.
I have done 2km swims, towing a buddy, at night, without lights,or a flag, and made it home safely. Of course it was August in Wisconsin which means that our water surface temp was around 28 degrees and not the 4 degrees that we have now.:waterwork
My father-in-law has done 5km swims, at night, without a flag, after his small boat sank, and made it to shore safely- only to be arrested because the cop on duty thought he was smuggling in drugs by scuba diving in the middle of the night. He made it home safely, but the water temp was around 15 degrees and he was wearing a full drysuit.
In the summer time, and even in the fall while we still have warm water temps, I think that a freediver can cover a lot of ground. That is actually one of the things I like most about freediving. I can cover a lot more turf than while on scuba.
Air temps do also make a big difference. We were out two weeks ago in 4 degree water, but we had some ElNino' air temps up around 10 degrees. That was pretty darn nice for around here and Ted even took two days off of work to enjoy it.
This morning the air temp is around -15 and I am not getting in any local lake this weekend.
In Eric's article he mentioned some of the same problems that Ted and I have had, mainly problems with hands and feet. I know that my feet would be especialy cold if I was using my mono in the winter instead of a larger pair of bi-fins with thicker booties.
I agree with his idea of cutting a whole and going for some depth. You can make ice diving a very safe and, relatively, warm experience. To swim out in the middle of the ocean at night is more of a test of wills than a fun outing in my own opinion. TO dive through a hole in the ice is a nice group outing.
Long swims are great, but Canada, like Wisconsin, are known to have some cold weather in winter.
Just my $0.02
Jon