The good news is that yesterday the app was updated to version 1.01 and most reviews are now positive. The crashes have been pretty much fixed, and the audio streaming is working very well. There are some scattered complaints about the game day pages being a bit behind, but generally people are now very pleased.
In my tests of the first version, I had lots of crashes, and indeed, the audio streaming was spotty. The new version has been crash-less so far, and the audio has been smooth and starts up quickly. I've listened via WiFi and 3G with no issues -- although if you are trying to use the app from your local ballpark, as Steve points out, you'll be competing with thousands of other fans for scarce 3G bandwidth and you may not be able to use the audio features (or do other things involving the cell connection, like making and receiving calls).
The app itself is a bargain, since getting audio from any game all season long costs $14.99 via MLB on the web. For 5 bucks less you get it on your phone. If you can live without streaming audio you can get MLB.com At Bat 2009 Lite for free. Now, if my hometown team just wouldn't come in last again this year all would be well. I guess the iPhone can't fix that.