Let me tell you something... if you've built yourself a simple iPhone Web App... and you'd like to get a few hundred users REAL QUICK... SUBMIT YOUR APP TO THE APPLE WEB APPS DIRECTORY. Run. Don't walk. Run to the Apple Web Apps site and do it now.
I about fell out of my chair after submitting my app late one night only to wake up to 100s of new users. Upon checking the directory, there it was... right on the Apple Web Apps home page as a "Staff Pick" - "Mila's Tools", my new iPhone Unit Conversion App.
Pure awesomeness, drenched in awesome juice.