I'm finding that the sound file attached to the sample sentence does not correspond to the sentence. There is a working sound file, but it is consistently for another sentence. Is there something I can do to remedy this problem or is it a systemic problem?

We're working on this with the gracious text-to-speech provider, Tingwo. Their guy was on leave for a while, but we hope to get a fix on this for you soon.

This has been happening to me too for a few weeks now. Not always, but I'd say usually when I click on a sample sentence the audio is wrong.

So were you not able to get this working again?
The text to speech for sample sentences seems to have been completely removed now.

Yup, I've removed it until we can get a fix, as it's causing a jillion bug reports. We're still working on it, though, and if you want to try your luck, you can head on over to beta.