The comment under these photos on the ILBIRDS forum giving the bird an index score between 11 and 12 is, I would say, overly generous. The undertail coverts that we can see (not much) seem to show a small dark streak on one of the smaller undertail coverts coming up along the side of the tail. So the score for that would be at most 3, and more likely 2. The flank streaking looks solid and broad, with about equal dark and white bands, so I would put that between 2 and 3. Only a tiny fragment of the rump is visible (the index is only meant for the rump, not back color). What we can see is a few gray marks on the lower rump, which puts it at most 4, and possibly 3 or even lower. Note that redpolls tend to have more white on the lower rump than the upper, so it's possible that this bird could move its wings and reveal a heavily streaked upper rump like index 2. So I would say the highest possible score for this bird would be ten, and more likely something like 7.5.
If we can use Troy's numbers with this index, this bird should be called intermediate, and closer to Common. All that being said, the frosty-gray back is another feature suggesting Hoary, so maybe that tips the balance a little more towards Hoary. This is a bird that, if seen in northern Alaska, would probably blend just as easily with a flock of Hoaries there as it does with Commons here. I don't think we should call it a Hoary, but at the same time it would be incorrect to dismiss it as a "pale Common". It is intermediate.
For comparison, check out this photo recently posted in Massachusetts. This one scores higher on the index ( I'd say undertail coverts 4 or higher, flanks 4, rump not visible). Furthermore, the back is pale and grayish, and it looks pale overall. I would feel pretty comfortable calling it a female Hoary.
One other comment:
I see a lot of blog visitors coming from "across the pond", where there is a very interesting ongoing discussion of a pale redpoll on Birdforum and the Surfbirds forum. I'm sure it hardly needs to be said, but I would be cautious about applying ID criteria from one side of the ocean to the other. These birds are regionally variable - and the species differences we are talking about are so slight - that a small shift in the average paleness of one population will confuse the issue. The questions are basically the same, but the precise details of the answer may be different in Europe and North America. Just something to keep in mind.