Here's an interesting new product/service from Microsoft.  Let's take the "protection" aspect first...

You can purchase things called Permutations.  Each permutation is a new secure virtual machine, or SVM, which is unique to you.  Microsoft ships a tool called the Code Protector that allows you to pick key (sensitive) functions in your code, and it converts each of them to SVML, the secure equivalent of IL that is unique to your SVM.  Then it replaces calls to those functions with calls to a new runtime component that can invoke your SVM so that your protected functions actually run.

The literature seems quite guarded in its claims about the security achieved, simply saying it is harder to decompile SVML than IL.  I'd say it looks considerably harder - we're talking about cryptography I think.

That's "protection", but we also have "licensing"...

The service allows you to define products, and SKUs thereof, so that you can issue licenses for people to use your software.  Then there's an activation process (similar to activating Microsoft software I guess) whereby people who've obtained licenses from you actually make the software work for them.

Depending on the level of service you've bought (how much you've paid) you might get features such as the ability to track activations.  The idea of trial SKUs is supported.

The most basic level of SLPS costs $500 - I don't know what the UK price is yet - and for that you are allowed to configure licensing for one product, including 100 commercial activations, 1000 non-commercial activations.  You also get one permutation that allows you to protect up to 5 functions.

If you're an MSDN Premium subscriber you are eligible for a 12-month SLP basic edition (what I just described).

If you have the infrastructure (and the cash) you can purchase SLP server products to host yourself.  In that case your users connect to your servers to do their activation, etc.

For more information, see...

http://www.microsoft.com/slps

http://msdn2.microsoft.com/en-us/slps/default.aspx

The actual online service is at...

http://my.softwarepotential.com

...but you will need a product key for SLP in order to use it.