Now, I'm not normally one to "read into" people's comments, but it seems to me that both tweeters may be hinting at subtly what they cannot say outright: That Williams will announce Google's acquisition of the microblogging service on the Oprah show or sometime before the show.
Williams said initially that tomorrow will be a "very big day" -- not just a "big day." When he specified Oprah, he said it was just a "big day." Being on Oprah for a guy who's on major TV shows almost every week makes it a "big day." Being on Oprah and announcing a Google acquisition probably qualifies as a "very big day."
And Kutcher has only 140 characters or less to tell fans he's going to be Twittering on Oprah, and in that cramped space references "search engines" followed by "LOL"? Unless we're being punk'd, I'd say that was a pretty blatant hint.
If so, they're not the only ones dropping hints. Google CEO Eric Schmidt conspicuously "heaped praise upon" Twitter today in that company's earnings call. There's no way he'd be doing that unless he wanted to secure a major deal of some kind with Twitter, or has already done so.
Any of these hints by itself wouldn't mean anything, but all three together make me believe that the rumored acquisition hits tomorrow.