It's available today as a free public beta. I downloaded it immediately.
Notes so far have been limited to the following:
- The sign-in and sync services take a bit to look for, but they're in Preferences. (They work, too. All my podcasts and their current episodes showed up, although I had to play with it a bit to get it looking exactly like it did on my iPhone.)
- There's no "download" button, either - that's accessible via right clicking.
The thing's light, fast, and OS X 10.8 Mountain Lion only. I've been waiting for this since I downloaded Instacast on my iPhone.