http://raventools.com/studies/onpageseo/

Some highlights:

• 78% of issues are image-related
• 83% of pages use Google Analytics (meaning 17% don't!)
• 29% of pages have duplicate content (Panda, much?)
• The most common onpage issue is not having a <title> attribute

Knowing this, do you plan to focus extra attention on these topics for your clients?