With the small limitations of this, it is mostly a novelty--what makes it interesting is that most FPGA's are much more expensive than $5. So that's cool. Maybe

With the small limitations of this, it is mostly a novelty--what makes it interesting is that most FPGA's are much more expensive than $5. So that's cool. Maybe you could implement a SPI slave to I2C transceiver or something like that -- something not so easy to do, but useful for a design. And yes, with only the OTP memory, the external EEPROM makes it more expensive. So at the end of the day, why not just buy a cheap micro for $0.75 with built-in flash, multiple blocks to do cool stuff, and if you are dead set on doing some FPGA type stuff, Cypress Semi has some psoc devices that have built-in logic blocks that are similar to FPGA macrocells.