We just got back. We initially flew LHR/SEA on BA then on to Juneau and Skagway crossing the land border to Canada on the White Pass & Yukon Railway then back into the USA a few days later along the Alaska Highway. After some time we got a cruise back from Seward (south of Anchorage) to Vancouver BC and then YVR/LHR on BA, I filled in my ESTA, only got a customs form on the plane and the immigration man just stamped my passport.
We crossed the border from Canada to the USA on the Alaska Highway as part of a tour group. The Tour Manager said they kept changing the requirements. In this case an agent came on board, looked at us all, asked the tour manager to gather all the passports (ours were the only UK, there were 4 Canadian and the rest (42?) US). She disappeared into the office for a few minutes then came back, gave everyone their passports and we passed through.
On the cruise we were given a briefing piece of paper the night before we arrived in Vancouver which effectively said we needed to give up our I-94W which we didn't have. I got two completely different stories from the cruise personnel neither of which was true (I am writing to the cruise company).
When I got home I checked with the CBP website and used their contact us service. They have confirmed we left the USA when we left the cruise.
So, it all seems to work, even in slightly complex scenarios.