First, before anyone gets all worried about the privacy stuff - you can't read the chip without manually entering some of the info from the passport. So, this info cannot be obtained merely by waving the smartphone near the passport.

Other than having fun, the only practical use I can think of is determining if a passport is genuine and/or whether the information was altered or photo substituted.

I just got a new Galaxy Nexus with NFC (near field communications.) I was having fun reading a Clipper Card (kind of like an Oyster card used in the SF Bay Area), and decided what to see what it could do with an epassport. It does more than I thought, here's how to do it (assuming you have an Android smartphone with an NFC chip.) I tried this on a German passport and it worked, the phone could not see the chip in a US Passport that I tried.

First, download the following from the Android market - NFC Taginfo and passportimagedecoder. Both are from NFC Research Lab.

Start up NFC Taginfo, and hold the passport near the phone. It will see the passport, and give you some info about the chip, but no data about the passport holder. There is a place to enter the following info in the app: passport number, DOB of holder, and expiration date. Enter that information.

Then start again and hold the passport to the phone. This time you will be able to see on your phone the date of issue, birthdate, issue date, expiration date, country of issue, and nationality of holder. You will also be able to see the photograph from the passport.

As I understand it the reason for requiring the information first is that this prevents scanning passports of nearby people and scraping the information. However, it allows someone with the passport in hand to verify that the info on the chip matches what is on the passport, and that there has been no substitution of the photograph.