On Jan 1st, there was a flurry of reports about a serious SMS bug affecting Android users. Google identified not one but two rare bugs, causing unintended behavior. One issue leads the wrong message to be displayed when you tap on it, the other actually sends the message to the wrong person. Fortunately fixes for both of these problems are on the way.
Google will likely distribute the fixes over the air to the Nexus One and Nexus S, and users of other devices will have to wait for their manufacturer to release an update (which hopefully will happen quickly).
Here's the update in the bug tracker: