Vitaliy Kaurov at Wolfram:

When Does a Word Become a Word? “A shot of expresso, please.” “You mean ‘espresso,’ don’t you?” A baffled customer, a smug barista—media is abuzz with one version or another of this story. But the real question is not whether “expresso” is a correct spelling, but rather how spellings evolve and enter dictionaries. Lexicographers do not directly decide that; the data does. Long and frequent usage may qualify a word for endorsement. Moreover, I believe the emergent proliferation of computational approaches can help to form an even deeper insight into the language. The tale of expresso is a thriller from a computational perspective.

Adventures in Computational Lexicology indeed.