It annoys me to no end when people decide they want to use Latin to sound more educated, yet can't take the trouble to make sure they're using it correctly. The most common instance of this is probably the confusion of i.e. (id est, "that is") and e.g. (exempli gratia, "for example"). I don't know why the former is so often used when the latter is correct. If you aren't sure, for goodness' sake, just use the English!
During my graduate work I often had discussions with my colleagues about so-called ab initio calculations, referring to those performed "from first principles." My professor was fond of describing our own work jokingly as "ab nada," never mind that he was mixing a Latin preposition with a Spanish pronoun. I tried getting him to say ab nihil instead, but to no avail.
And finally, what's the deal with the name of the Internet used book seller Alibris? I assume it's supposed to trigger an association with the expression ex libris ("from the books"), but the preposition a also means "from." I've never seen a libris (or ab libris) used in this manner and can only assume it's not idiomatic. If the company's name is supposed to mean "to the books" instead, it ought to have been named Adlibros.