On more than one occasion now I've sent text messages to my girlfriend from my Pre and she doesn't receive them. They show up in my chat window as sent after they're grayed out during the sending process. All looks well but then she never gets it, and it disappears from my chat window on my Pre sometime later. (No she's not deleting them from my Pre and she's not lying.)
This never happens from my Treo so I don't think it's a Sprint issue.