Sorry - that title should read HOW do you figure out Named and Floating for AC and SC.  Thanks!

I try to explain who we do it.

If you have staff working day by day you should use named users. Others should use floating licenses, that means approx. 5 Users are sharing one floating license. For an exakt calculation you should define a profile for every user and estimate usage time and intervall.
The Get.IT User are licensed seperatly and are 10% of the total amount of users.
They are using not directly AC or SC, the access is via Get.IT.

Exactly - the count is 5 floaters to one named. It is up to you to determine who needs to be named users though, each shop is different.

Thanks
Big Tex
http://clubs.yahoo.com/clubs/peregrineservicecenterforum

Named user licenses should be assigned to people who will be logged into the system for most of the day eg helpdesk operators taking calls - OR to people who MUST be able to login at any time.

Floating users are for every one else and will depend on how many tickets you get.  The floating count will generally be one license for every 5 operators - but you will need to determine work practises etc (if most of your second or third level support people only look at 3 or 4 problems a day they do not need to be logged in very often and therefore you may be able to go above 1 for 5.  If however they are fixing 30 or 40 incidents a day then you may need to go as low 1 to 2 or 1 to 3.

If your work flow allows notifying people via email then this enables a lower usage count - as you can include enough details that the techs don't need to login to sc to see their queues.

This answer probably isnt the most technical in the world..
Check the pricing of the licences
Find the cheapest and buy them! Floating can act like fixed licences if you have the right number of them.

Believe me nothing will get the system a bad name quicker than not having enough licences