[chrisuk]

How is is parasitic when the site is performing a service and saving you money?
I have used several before and I agree its infuriating when the code has expired or isn't there.

Aside from that they are pretty darn useful giving the user exactly what they want. I ordered pizza the other night and got 25% off so no brainer really. if people want a 1-stop resource where they can save a packet then how is that not a good user experience?

Like with anything, shopping comparision, arbitrage, cashback there are good implementations and not so good ones. You have have to accept that with the wheat there will be some chaff.

Also how many merchants run adwords or seo for products they don't sell in order to capture traffic. I doubt many voucher code operators consider themselves 'lazy ass.'