There's an update to Adobe Digital Editions available. This update fixes a number of bugs, adds support for Windows 7 (32 and 64 bit) and for Mac OSX 10.6 (32 and 64 bit), but also removes support for Content Server 3. Read the Release Notes (PDF)
Note that on Windows, when I ran the older version, a dialog came up asking if I wanted to update. What I didn't realize (at first) is that clicking yes simply loaded up the Adobe Digital Editions website in a browser window, from where you must explicitly choose to download the update.
Also, for Mac users, there's a warning that the installer does not remove the previous version; you have to do that manually.