Via Paul, Twitter are changing their search API to return relevant, as well as / rather than recent results. This has caused immediate complaint from developers, of course. FEAR CHANGE.
But for the record, I agree with the complaints.
search has always returned recent results. Twitter is commonly used as a stream-of-world-conciousness service, and returning recent results makes sense in this picture. Much more importantly, changing a shipped API to return a totally different sort of result is just not on. Their response to this? It's not going to happen right away. Great.
Here's a theory, one that I've been tempted to apply to facebook recently as well. Maybe Twitter are intentionally trying to keep the concept of 'backwards compatibility' slightly fluid. You keep your developer community on edge all the time, force them to be able to release updates on a moment's notice, force them all to subscribe to the API group and watch for changes, instead of just releasing an app and wandering off to do something else. It makes them more likely to add other features, keep their apps up to date, keep the buzz going...