Throughout my wedding planning process, I have gone back to The Knot time and time again for help with various aspects of the ceremony, reception, transportation, and everything in between.
I have utilized the accurate, honest vendor reviews from other brides on multiple occasions on the message boards, and gotten solid advice about how to handle various situations. I can usually rely on the honest, straightforward responses of the others. Even my fiance has said "ask the girls on The Knot about {insert situation here}."
I have also utilized the customizable checklist. That has been a good reference for making my things to do list for everything wedding related. The budget tracker is also quite helpful.
My only issues with The Knot are basically that updating profiles, etc. is quite difficult. It needs to be more user friendly, because not everyone is an expert at writing internet codes, which is required. If that were made more user friendly, I think it would add a lot to the site.