As far as getting books from a Mac to the iPhone/iPod Touch, it’s very simple, just not intuitive.
To do that, you open your book in the desktop app, go to “Tools”, then “Enable Sharing.

Now go to your iPhone/iPod Touch, Click “Shared Books” click on your computer’s name, then click the title of the book to download it. This usually takes 1 to 3 seconds, depending on the size of the book.

I’ll be posting a full review of Stanza to my website later today.

The speed is very good when you switch pages and it takes a little longer when you get to a new chapter. That’s because in ePub, one of the best practices is to divide your e-book into multiple XML flows. When you access a new flow (a new chapter for example) it takes a little longer to load everything.

The problem with the iPhone is that there’s no easy way to get your own files on it. The filesystem itself is locked and applications cannot add a MIME handler for Safari (if they could, you could browse any website, download an e-book file and read it on your iPhone). Because of these choices Apple made, you need to run a server application on your Desktop to send your own files. It’s the case with both Bookshelf and Stanza, eReader haven’t released such software yet.