I haven't used it for ages now, but I have one of the ones with wires and pads you can stick on whatever bits you want to work. Instead of the 130 quid it should have cost new, I got it for a tenner on eBay. They won't make you thinner or give you more defined muscles and they're not a magic shortcut but they can be useful for rehab and strengthening. And for 'lazy' workouts. Ahem...
When I was working really long hours and was sleep deprived and short of time, I often used to skip my usual ab routine and instead go for an hours sleep with the pads stuck on and the machine turned up quite high. I got very good at sleeping through a thousand electrical crunches and it definitely did improve the strength of my abs.
Edited: 22/11/2012 at 22:05