Although in awe of the power of the interwebnet thingy I am always slightly suspicious of talk to promote e-democracy. As Guido says, it's just not the same as the real thing.
Having recently stumbled across Hear from your MP I'm less cynical though. You sign up with your postcode and email address and as soon as a proportionate figure (for my constituency 25) of your fellow voters have signed up the site is triggered. Your MP gets an email encouraging them to contact their constituents through the list and I suppose the idea is that the list will grow and you will slowly build a component of the "e-democracy". In fact, the reason why it might just work is because it supplements and facilitates the real thing - rather than trying to replace it.
So, if you live in West Worcestershire and your MP is Sir Michael Spicer, or if you live in the Cities of London and Westminster and your MP is Mark Field go sign up!