In my previous blog post I outlined some new commercial terms for Windows Live services that we announced at Mix. These are important because they give developers simple clarity on how they can use our services - and of course because the terms are so generous.

However I thought it worth drilling down on them a little bit to make sure they're as clear as possible. Do note however that the official word on the Terms of Use is as displayed on http://dev.live.com, but hopefully this explanation will provide some additional insights.

Oh, and this is all good news, I don't think you'll get any nasty surprises from the following :-). So here goes:

1. Silverlight streaming, Live Spaces API and Live Contacts API are completely free to use until they come out of beta. So all of the charging information I listed only comes into effect when these services go live
2. When we're talking about the Live Contacts API, the terms I mentioned (eg free if you have less than 1 million unique users per month etc) only apply if you're using the API itself. If you're using the Live Contacts Control - essentially a control you can embed within an iframe on your site - then these limits don't apply. Obviously the API is a more attractive option for many people because it gives you full control over the look and feel etc, however the control is extremely simple to use. The key point though: if you use the control, you don't need to worry about the usage limits.
3. When I talk about unique users, it's only those users that actually make API calls via your site that count. It they are just visitors to your site and they don't make any Windows Live API calls then we're not counting them
4. And it doesn't matter how many times they actually use the API within each month, we only count them once. So if they're constantly coming back and forth to your site and causing API calls we still only count them once per month.
5. Which also means it doesn't matter how many API calls they make - they could make thousands - we only count them once per month.
6. Another piece of good news, we actually take a 3 month average in terms of counting unique users, and usage of the 4GB limit. So if you have spikes of usage in 1 month say, but they drop well beneath the usage / storage limit in the other two months, you're fine as long as the 3 month average is below the usage / storage limits.
7. And one last piece: The incredible 3 million map tiles per month you get with Virtual Earth includes commercial usage. So if you find a way of making money out of Virtual Earth, but stay within the 3 million maps tiles per month number, you still get it for free.

The more I hear about this stuff the better it gets. What the Windows Live team has done here is really set the bar in terms of generosity of service use and clarity of the conditions. And the good thing is the deeper you look into it the better it gets, contrary people's expectations. This is terrific stuff.