Charlotte,
I used design forms, checklists, or worksheets for a very short while early on in the development of our business and just found them to be kind of pointless and more work for myself and the client than they were worth.

Now, I simply ask the client (via email) a series of questions about what they like to see/use on the web (a few favorite domains), what they don't like to see, what they envision their website 'doing' (for specialty features), and if we're building and integrating a user-interface like member registration or a shopping cart or similar I ask them what they envision their user's process is from start to finish.
From there I can reply with my vision of what's going to come out of the project, reiterate their wants in my own words, and add anything I think is necessary or explain why I recommend not doing anything in particular that may have come up.
I also always ask about keywords and have them send me links to their top three competitors - this is crucial for on-site SEO.

If they have a site already and just want a redesign, I ask similar questions but provide my own take on what could/should happen earlier on, make suggestions based on what I can see, etc.

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