I am listening in at the Marketing Sherpa B2B Lead Generation Summit #sherpab2b09.  (HubSpot TV is live streaming the event if you want to tune in.)  Here are some notes from the landing page session run by Flint McGlaughlin from MarketingExperiments.

Top Landing Page Mistakes to Avoid

1. Lack of Clarity - Do people visiting your landing page know (a) Where am I? (b) What can I do here? (c) Why should I do it? 
2. Undisciplined Eye-Path - Make sure you lead people's eyes in a single direction towards the action you want - try a page with a single column or at least one big column in the middle.
3. Insufficient Value Promise - Make sure the message on the button and headline talk about the benefit of completing the form.
4. Excessive Friction - Do your best to eliminate steps, questions and friction- try to balance quality and quantity.