Twitter! Whether you use it or not, or understand it or not, it’s the hottest thing in Silicon Valley right now. It’s brought up in every conversation. And no wonder - the service has exploded to somewhere north of 25 million users and has been growing by 40% a week since that Oprah appearance, says a source close to the company.

Google tried to buy it but was rebuffed by Twitter CEO Evan Williams, says a source with knowledge of the talks.

Today, though, rumors popped up that Apple may be looking to buy Twitter. “Apple is in late stage negotiations to buy Twitter and is hoping to announce it at WWDC in June,” said a normally reliable source this evening, adding that the purchase price would be $700 million in cash. The trouble is we’ve checked with other sources who claim to know nothing about any Apple negotiations. If these discussions are happening, Twitter is keeping them very quiet indeed. We would have passed on reporting this rumor at all, but other press is now picking it up.