I got a question about updating of custom fields and outline codes that was very Project Server 2003 centric in the way it was asked.  Instead of answering the question let me give a quick tutorial on custom fields in Project Server 2007.  This will in essence answer the question, and probably create a bunch more questions J. 

Custom Fields are no longer defined through the enterprise global.  All customer fields are created, edited, deleted… through the PWA administration screens.  You no longer check out the enterprise global to edit a custom field.

Outline codes no longer exist.  There is a new entity called a lookup table.  Lookup tables can be associated to custom fields giving them the Project Server 2003 outline code functionality. 

All major entities in Project Server 2007 are identified by GUIDs, Projects, Resources, etc.  Custom Fields are no different.  Big deal why is this so important?  Today in Project server 2003 if you write software that uses a custom field there is no guarantee that somebody else won’t be already using that field (EnterpriseProjectText10) when you go install the software.  Now you need some mapping utility to take that into account.  In 2007 when you define the custom field, the ISV defines the GUID for it.  At installation time the software installs the custom field using that GUID and now your software can DEPEND that it will find the custom field in that location (i.e. GUID).

There is no numeric limitation on custom fields.  Today you have ProjectText1-40, if you need 41 you are out of luck.  There is no theoretical limit to the number of custom fields in the system.  BUT the product group will limit the number based on performance.  It will be a big number though when all the dust settles at RTM.

Your custom fields can be defined with formulas and graphical indicators attached to them just as always.  The big change is now they will update server side!  No more having to fire up Project Professional to get that one calculation to take in that one field.

Enterprise custom fields have always been a big tool in the integration with and expansion of Project Server.  But in Project Server 2007 I think their usefulness has grown exponentially.

BTW all bets are off for local fields, they do not operate like the Project Server fields.  They operate the same way they always have.