Spotted in the MAKE Flickr pool:
Micah Dowty was frustrated with how poorly his sewing machine performed at slow speed, so he decided a sewing machine retrofit was in order. After adding a speed sensor, modding the foot pedal, and adding a beefier DC motor, he finally has the tool that he needed to produce cool projects, such as soft circuit RFID tags. He has a full explanation up on his blog, and more photos in a flickr set.
That is a great idea. I have about a half dozen sewing machines that could use an upgrading.
Remember u should never sew on a machine that is young than you!