I have lived in my house for 3 years, and just got my carpets cleaned. They did a great job, and they look so much better.
One tip though that people never think of to do is to vacuum your carpets when they are finally dry. They can never get the carpet 100% clean, without soaking it. But after they clean, they do pull up some dirt to the surface. I have 600sf of carpet, and this is how much dirt came out once it was clean and dry.
So just give it a quick vacuum.