Hmm, Stanza on the iPhone has been working ok over the few days I've been using it.
It did crash a few times, but that was no big deal, as it dosen't crash the whole phone (Something apple got right)
The major problem, being a Windows user is the limited functionality in the Beta Desktop Client. Having to have each book open as opposed to just being able to share a folder is a pain. Even having the ability to batch the sharing would do, but is not there yet.
Another pain is that there is no way to edit the Metadata (as Far as I can see) on the desktop client, so is the data when opening a file is wrong, the only way to edit is to download it and edit on the iPhone itself.
Still, for a Version 1 Product its looking quiet good, and shows a lot of promise for the future.