Disabling fields has been a great way to lock down information within MSCRM. The one issue that I run into with it is that users comment that a disabled field is so "washed out" that it becomes difficult to read.
Another option to use instead of the out of the box disabled, is to make the field read only. It's a very simple script:
crmForm.all.fieldname.readOnly = true;
It leaves the field looking like other fields so that it's not washed out but it cannot be edited from the form. This customization is technically unsupported, but it has been around since the MSCRM 3.0 days and so far Microsoft hasn't locked this script down. We'll find out next version whether or not the script gets carried over or not. But worst case scenario for your scripts would be that they need to be modified to use the disabled option rather than the read only option.
Dynamic Methods Inc.