Just to be clear, customers won't know their mtDNA haplogroup when we get our raw data for the autosomal test. Mitochondrial DNA is a completely different test.
(The sentences were semi-linked in Roxanne's post, which might imply a relationship between the two to some readers, so I thought I'd butt in and mention that.)
Secondly, having Scandinavian ancestors is not the same as having Viking ancestors. Ancestry likes to paint a romantic portrait, but not every person in Norway (etc.) during the Viking Age was out on the seas, sharpening their axes and talking about the good times they had last weekend plundering the monastery. Some people just stayed home and did the blacksmithing and farming and whatnot like ordinary folks.
But that kind of partypooping logic doesn't sell pie charts to eager customers. ;)
The autosomal test's raw data won't reveal "Viking" ancestry, either. Scandinavian-ish under an assortment of labels, yes, and you can make assumptions from there, but that's it.
I often use the term "Viking" in a tongue-in-cheek way to refer to my Scandinavian ancestors, so I don't mean to be humourless on the subject. I'm just being cautious since some people who are still figuring things out may take Ancestry's words a bit literally. :)