"Blog" has been served at Minicon for as long as I can remember (1973, I think). It's too sweet (all that grenadine), but has a strong acid backbone (all that citrus). It's alcoholic, but not spectacularly so (12 ounces of vodka to 170 ounces of mix, not counting the ice melt, making it 2.6% alcohol by volume assuming 40% alcohol by volume vodka). It's a tradition.
As the people involved in Minicon have changed over the years, there's been some drift in the recipe now and then. I think the recipe given here is in fact the original one.
Blog is widely rumored to have originated as a punch recipe learned from Jim Young's mother. Several people think it was first used at Minneapolis in '73 parties back when Minneapolis was bidding for the 1973 worldcon. Jim Young himself doesn't remember. If you have first-hand knowledge to share, please write us!
I believe this is the canonical recipe. Geri Sullivan says that David Wilford told her that this is the recipe Gin Nelson published in Rune #77 (and, in fact, later research shows that is indeed in Rune #77).
If you omit the vodka, it's called "St. Paul" blog. The normal version should not be called "Minneapolis" blog, however; it's just "blog". Period.
For obvious reasons, nowadays we use 4 liters of ginger ale instead of 4 quarts. When was the last time you could get a quart of ginger ale? The difference, if you're wondering, is tiny: about 7 ounces (or 200 ml).