I'm having similar problems - the dictate actually says 20 seconds recorded after about 4 seconds and of course playback is then really slow.
Scribe is having a problem too - it is degrading after 5 minutes to unusable. Quitting and restarting works but this is tedious -
I'm wondering is it because the app is running under rosetta and is not a universal app yet?
It's frustrating as the dictate / transcribe solution is rapidly becoming a big problem.
We are using macbook pros and intel imacs running 10.4.6
Any ideas?