A recent "Ask Slashdot" asked what information a sysadmin should take to an executive. Here's what I think. I've picked this up from a variety of sources, including a very-skilled manager.
There are three key things that executives want to hear:
1) What has the department done in the past? The core of this point is to get to the question "Does the past justify continued investment?" and its correlary "We've sunk so much money into IT, what have we gotten from it?" This is where usage statistics (website hits, business transaction data, dollars-per-downtime and Nines, return on cost-saving measures, etc) are presented. This should be in high-level terms with drill-down slides available, but only presented on request. Focus on the trends of service delivery vs. IT budget and/or headcount.
2) What is the department doing now? Here we focus on what is happening with their current business. This is where a primary element of capacity planning comes in: The Headroom Metric. How much additional user load can we support on our current systems and network, before the service is degraded? In concrete terms, ignoring everything except CPU, if you're delivering 100 pages per second, and using 40% of the server's CPU, you have a headroom of 150 additional pp/s. By extrapolating this to the business need - say the marketing department has launched 5 campaigns this year, the current systems may be able to support 10, but should not be expected to support 20 without additional investment. Note that this headroom metric must look at the end-to-end utilization, like disk, memory, network, and most importantly administration effort in order to be accurate.
3) What will the department do in the future? What are the business-focused projects that the department is working on? How will the investment in these projects result in money coming into or staying in the business? What is the Return on Capital, Return on Investment?
As far as timing, there should be at least an annual "full report" on the state of IT. Depending on the dynamics of the business, quarterly updates should be sufficient, unless something changes significantly. And depending on the team and scope of the projects. You don't want to face this with a "we haven't done anything since the last report" status. But it's also important to reconnect with the executives regularly so that they don't forget about what you're doing, and also so that you can react and change to meet their changing business plans.
The most important thing we in IT can do is to be aligned to the business. This means focusing on the things that matter: delivering the product or service in exchange for money. Everything else is overhead. And the better your IT department is at aligning itself, the better you look when an outsourcer tries to talk your executives into cutting everything except the "core competancies".