As a kid, I had a stamp collection. As a computer professional mostly dealing with data management, I have always been interested in how the USPS can route so many bits of mail so quickly for such a relatively low cost. As a result, news from the Postal front usually piques my interest.
Endicia released PictureItPostage for Mac OS X Tiger. It is a little (2.1MB) Cocoa & Quartz Composer app that leverages your iPhoto library to enable the creation of custom postage stamps. You can then buy sheets of said stamps from Endicia to splat on your various paper envelopes.
It is a neat little application. Given the 50 cent/stamp premium, I doubt I'll use the service for anything but the rare special occasion.