_UPDATE, 28 Oct: This isn't working right now and is very frustrating. I can sync a new database from either device but can't get the iPhone to take the latest from the MacBook._ Tonight I upgraded from OmniFocus 1.0 to 1.5 sneakypeek, purchased OmniFocus for iPhone, and set up free WebDAV sync using sharemation.
Downloading and installing the OmniFocus upgrade was easy, as was purchasing OmniFocus for iPhone from the app store. The first time I ran the upgrade it converted my database which took a minute.
Creating a free account at sharemation was easy. I did not create any folders there. To connect to the highest level folder using WebDAV from Finder, connect to "https://sharemation.com/username".
Next I set up sync for OmniFocus on the Mac. Knowing the URL, username & password that worked in Finder was all I needed. The first sync took a couple minutes.
The next thing I did was send my settings over. This did not go so well. I kept getting trapped in a loop of selecting between the local & server databases, or re-entering my sync username & password. I finally got out of this by syncing the local database from the iPhone to make a successful sync from there. Then on the next sync from my Mac I had to tell it to use its local database, not the blank one I'd just synced from the phone. On the next sync from the phone I got the right database down, I think because I didn't have to enter credentials again.
So there was a bit of hassle, but with some perseverance it seems to be working. And free. If I was doing it again I would back up my database, then sync blank or starting databases to get sync going, then restore the backup & sync it to the phone.