To "Google" or to "google"? To "Tweet" or to "tweet"?

According to Merriam-Webster, while "Google," a trademarked company name, obviously is capitalized, "google," a verb, is not.

Similarly, while "Twitter" is capitalized, its verb variant, "tweet," is not. As editor at large, Peter Sokolowski, explained in an e-mail to me today,

Tweet as both noun and verb, used to mean “update message” or “to send a short message or update,” is increasingly common and we’re watching the evidence. For now the word is largely styled lower-case. As with all words in our dictionaries, evidence of use for both the meaning and the styling of a word is the only criterion we seek.