For my highschool senior project I decided to redesign the TV-B-Gone, using Ladyada's model as a reference (http://www.ladyada.net/make/tvbgone/index.html).
The reference model was great, and still continues to function after two years. The problem was that it's too big. It's got a healthy nice heavy feel to it, but it's too large and fragile for the purpose it serves. Before I critique the design too much, I should note it's designed to be large so that it's easy for beginners to solder together.
Because it's supposed to be easy to solder, nearly every part is through-hole. Easy to solder, but huge and fragile. After putting it in my pocket a few times, a couple of the transistors broke off, rendering the outer two LEDs useless.
But I liked the idea, so I took on the challenge of redesigning it. Originally I hoped to have three designs: wide short range, narrow long range, and a combination. Each was to be powered by a coin cell or two, making the entire unit the size of your thumbnail. Unfortunately, while coin cells can deliver the required voltage they don't come even close to delivering the required amperage. Back to regular cells, and ultimately I settled on downsizing to two 'AAA' cells.