I'm running Lion 10.7.2 I believe, when I press play on the Speech->Text To Speech tab if I have my output in the Sound panel set to Internal Speakers/Headset and then press the Play Button on the TTS tab then I can hear the preview, it reads correctly.
However if I highlight text anywhere and use the key combo, I notice the blink of the cursor, I see the Speech Synthesizer Server in the processes, it does not hang, Though no sound comes fourth, no matter what the Output in Sound is set to.
Again however, if you select the text you want the TTS to process, and you instead use the Add To iTunes As Spoken Track Service, availabe under Service Preferences->Text it processes successfully no matter which installed voice you chose.
This to me seems like if you use the Key Combo some error happens where the text never makes it to the server, the server summoned with no text to process just sits there idle until you manually kill it, this is why the Play button freezes the preferrence window, it tries to launch another Speech Synthesizer Server, but it can't as I'm guessing that's a process set with a flag not allowing it 2 instances.
I posted all this in the hope that this may help my fellow users, and that Apple can get this issue pinned down and worked out, the last post to this thread was a MONTH AGO and it seems these people are sitting here waiting for any kind of official response even a glimmer of hope.
If anyone reading this has managed to fix it without posting how, PLEASE TELL US.