Tested version 3 and version 4 beta, July 2007.
Needs a JVM, which can be downloaded from here or here (should be version 5.7.2).
Appeared to be very unstable at first, the application plainly quit when the end user license agreement appeared, or soft-reset the Treo. These problems went away when I changed the JVM settings (Prefs->IBM Java VM) to use more memory (4Mb instead of 1Mb) and stack (32Kb instead of 4Kb). In the end version 4 beta was still unstable, it hung my Treo when loading a page that had been loaded before without problems.
It has the option to not download images, an option I missed in Blazer. In general it seems to render pages much better than Blazer. For example mijnpostbank.nl. A site both browsers can't handle is wikidot, unfortunately. Pressing the login button just reloads the page on both browsers. This means I can only view the stuff I put on there, but not edit it.
A downside of Opera Mini is that you can't set the start page to a different page. You can change the bookmarks displayed on the start page, but I like to start a browser with my own set of links. It's only one click away, but still. I'm also missing the find function on a web page.
In the end I'm replacing Blazer by Opera Mini 3.
