Gift Giving: It's been hunching within me for some time now, but I know it's hunched a full-grown hunch: in these last few flash fiction contests you've been writing
metalogues á la Gergory Bateson. The content of the conversation is the structure of the story is the content of the conversation... Bearing this in mind, I think your conversations might profit from "image control". In the present story: Why are they drinking? What are they drinking? When are they drinking (as opposed to talking)? [There might actually be a pattern to it I missed...]
The Joy's of Christmas: Oh dear, poor Matnis... There must be thousands of people around who understand (and millions who torment them).
Heavenly Peace: A very interesting story, hinging heavily on the song "Silent Night". A couple of comments from a native speaker's perspective (I'm Austrian and not leaving far from where the song was written): (1) You got the lyrics right; trouble is - barely any native speaker ever does. People tend to sing "hochheilige" instead of "heilige" (better text-to-rhythm match, I suppose); and "lockigten", though in the original text (I sometimes read "lok-kigen" to space out the syllables on sheet music). Still, most native speakers sing either "im lockigen", or "in lockigem" (which would be the most natural version). I have no idea what soldiers in the World Wars might have sung, though. (2) "Heavenly Peace" makes a nice title, being a quote from the song. The German counterpart, though, has different connotations, "Ruh'" being literally "no sound", and in extension "no movement, no disturbance". So, to me, on a metaphorical level, the English lyrics suggest actual "peace", while the German lyrics suggest more of a ceasefire (which does tend to be one of the kitsch interpretations of Christmas, oddly enough.) // Just random comments. The story is very well executed, and ends, as I read it, in a mixture of exhaustion, relief and disbelief.
A Christmas Wish: I can't say I get the "rule" behind the ending, and neither do I understand this line in the light of this ending, which sounds key: "Incidently, I was asked that very question once, a long time ago. My answer was how I came to be a genie." Shouldn't the final wish have affected the wisher? What am I missing? (I do like the cross-cultural wishing index you set up, though.)
Faraway Holiday: Solitude at Christmas - job related. Well executed, especially little Megan speaking; she comes alive. The ending's quite complex, too - all with just a book and a title. (One minor comment: I'm terribly fond of the "addressing comma". If I'd written this, it would have been "I'm Megan, Santa." Thus reading, "I'm Megan Santa," makes me think she has a felicitous family name.

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Merry Christmas Larry!: Noooooooooooooo! The scariest dystopia to date. *Shivers* (I must distract myself by pointing out another lack of an "addressing comma": "Merry Christmas, Larry!" Am I the only one who likes the "addressing comma"?

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Cookies and Milk: The kind, fat guy, and the carpenter. It's a consistently sentimental story that fits the theme very well. A low-key, subtle, meditative story, and a good read.
Letters from the Diaspora: Now, here's an interesting entry. I like the edited-letter idea. Kudos for bypassing any sort of sentimentality or cynicism. It's a simple letter and works as such. Can't judge historical matters; I know too little about the middle ages.
1200 Glenview Road, or, the Marriage of Time: An interesting take on time travel: alternate timelines under a superposition model rather than multiple worlds - which allows interesting takes on morality and consequence. In this case it's about the morality of presents. (And in the background hovers the idea of "White Christmas" when you can control the weather.) Intriguing.
Intercalary Christmas: People argue about Jesus' birthdate all the time, but few ever argue about Calenders. Heh. Nice job; santa has come. A day late and in disguise, but who's going to be picky when the present's great?

(Oh, and I didn't know the word "intercalary". So thanks for that as well.)
Nativity: Best opening line. An interesting and surreal story. Interesting shooting star metaphor, too. Though the ending suggests genesis more than Christmas, I feel. Still, full points for stunning creativity and great prose. (Isn't it "metric tonnes"?)
And now for the part I hate the most. Voting. And this time I have more candidates than usual, too. Grr... I'm in the pre-Christmas spirit.
Stress!
Anyway: I think I'll go for "Cookies and Milk" this time round. Can't tell you why. Perhaps because it's the least stressful of all the equally worthy candidates?
Well done, everyone.