Seth Godin is fed up with the traditional business plan, suggesting they're "often misused to obfuscate, bore and show an ability to comply with expectations."  Instead, he'd like to see the modern business plan divided into five sections:

• Truth
• Assertions
• Alternatives
• People
• Money

It seems to me that this breakdown would also be a great way to subdivide the traditional client status update (or case analysis) letter.  Instead of burying tons of information in multiple paragraphs, break down the letter into the five sections Seth suggests.  Your clients will better comprehend the information your giving them, and you'll have an easy-to-use template for all your client correspondence.