Many developers use Ad Hoc App Distribution to insure that beta testers and reviewers get copies of their software prior to the App Store release. A developer takes the Unique Device Identifier (UDID) from your iPhone, does a little magic, and then sends you two files -- one contains the app, while the other is a provision file. You drag the provision file to your iTunes Applications window, followed by the app file. A quick sync with your iPhone installs the app, and you're ready to go.
Alex has set up a website where you can sign up to get an Ad Hoc distribution of Podcaster. You'll need to "donate" $9.99 to Alex via PayPal to get the app. I think this is a great way for smaller developers to get their apps out there, particularly when Apple decides to shut 'em down -- although they are sharply limited in the number of licenses they can distribute this way, no more than 100 devices total are allowed.