Vocitated

Meaning: named or called.

Usefulness: 2 (It strikes me as a satisfyingly annoying way to ask someone's name "And what are you vocitated, old chap?" or introduce yourself: "I am occasionally vocitated as The Antipodean.")

Logofascination: 1 (The English version was invented by Sir Thomas, who is the sole citation in the OED.)

In the wild: Occasionally; someone's already taken it as a Twitter handle, worse luck.

Penitissim

Meaning: Innermost.

Usefulness: 2 (Could lead to some confusion if used carefully, which Rabelais might have been counting on.)

Logofascination: 1 (Originating in Pantagruel, this is probably a Rabelaisian coinage, although it's from a common enough Latin root, penitus. The OED has Sir Thomas' Ekskybalauron as the sole citation, since it is the main English source. I can't help but wonder if it's in the OED to help explicate Rabelais, much as most of Cotgrave exists for that purpose.

The really fascinating thing about this word, though, is that Ekskybalauron was published before Sir Thomas' Rabelais translation - they are only a year apart, but this suggests that he was already working on the translation, and had thought about how to Anglicise this passage.)

In the wild: Besides the piece on neologism I linked to recently, it's also cited in a rather useful dissection of the original.

Flagitious

Meaning: very, very nasty; usually used in association with crime: "flagitious crime".

Usefulness: 1 (Sadly.)

Logofascination: 1 (Fascinating, but confusing; although at first glance I thought it would be a cousin to flagrant, it seems to be more closely related to flagellation. The OED links the flag- back to the same root as flagrant, but etymonline has different Proto-Indo European roots for them. The OED entry hasn't been updated since 1896, so I'm going with etymonline, meaning that etymologically, this refers to crimes resulting in scourging.)

In the wild: No; I'm rather suprised newspapers and politicians haven't resurrected it.

Supererogate

Meaning: to do more than required, to go beyond; originally a Catholic term referring to someone performing good works / penance / prayers to earn merit for another (e.g. a deceased relative).

Usefulness: 1 (Sarcastically: "Well, no need to fear supererogation in this office." To confuse waiters: "Your supererogation has not gone unnoticed.")

Logofascination: 2

Quadrantids

Meaning: it's a meteor shower which occurs in January, and is named after an obsolete constellation (do constellations get severance pay?), Quadrans Muralis. The Quadrantids now live in the Boötes constellation, but have kept their original name. Boötids certainly doesn't have the same ring to it.

Usefulness: 3 (you wouldn't get to say it much; useful if around astronomers, in need of a particularly difficult trivia question, or looking for a name for an alien species in your latest SF work)

Logofascination: 1 (it just sounds lovely)

Flay the fox

Meaning: Cotgrave gives us a definition and the only etymological speculation I can find online:

"Escorcher le regnard.  To spue, cast, vomit; (especially upon excessive drinking;) either because in spuing one makes a noyse like a Fox that barkes; or (as in Escorcher) because the flaying of so unsavorie a beast will make any man spue." (Current French would be écorcher le renard.)

Usefulness: 3 (depending on your lifestyle. It should be noted that flay the fox sounds suspicious even if you don't know its meaning, so the French version could be useful if you need to describe a particularly good or bad weekend in front of the boss.)

Logofascination: 2 (mainly because it's slightly mysterious slang; I'm not quite sure what it is about old terms for bodily functions, but they're popular.  Jonathon Green has written an almost poetic list of synonyms for vomit, and points out that Australians have originated or are the main users of 38% of these terms. Having recently translated the lyrics of Land Down Under for some Americans, I can't comment.)

Eleemosynary

Meaning: charitable; related to charity, alms or alms-giving

Usefulness: 2 ('eleemosynary works' could be listed as an impressive hobby, or it could be used to obscure political arguments - see below.)

Logofascination: 1 (it's the double e, I think)