An over-the-air update is now being pushed out to HTC Legend owners to fix a bug which makes certain apps vanish from the Android Market. According to HTC this is due to a camera issue but the update should make things all better again.
Update – There is also an update for the Desire delivered over the air. This was initiated a few days back now but new customers may see it popping up. If you haven’t got it or want to check for these things manually, go into Settings -> About Phone -> Software Version to grab it manually.
Link – HTC Support