We have been debating the idea of using custom fields to give our customers more options for their products. One of the main issues we are looking at is dealing with adding names and numbers. This works perfectly with custom fields since not only do they not have to be required like normal text but they also will show up at the checkout level in the cart so customers can see all the way through that they are getting what they typed in. The issue being we woudln't be able to charge them extra for doing so.
It could also be useful for other features like do you want gift wrapping +X dollars with checkbox fields and such other great ways to build on custom fields