There is (almost) no difference between one Domain Admins member
and another, except that they are different accounts. The domain account
named Administrator (initially) has a couple differences.
In my opinion, if it is accountability you are after, you should not be
sharing an empowered account between people, except under very
restrictive policies. Rather, give each (of the hopefully very few)
an individual account, and a set of guidelines for acceptible use.
Only used one x, y, z machines - no log on elsewhere; only used when
that priv is necessary, not used otherwise. etc.
The best thing however is to not provide Domain Admins membership,
but to look at what these people each do, and delegate to them. There
really is only a small amount of things that must be done with a Domain
Admin account, or even with an account that is member in the domain's
Administrators group (which is quite different from Domain Admins an
has a much more restricted scope of privs).
If you must share and account, make it so it can only log in at specific
consoles, and the process for gaining physical access to those will
help document who what there when.
Finally - every administrator should know that changing the password
of any other account _is_not_to_be_done_ , even for just a plain user,
except as a last resort. Resetting the password of an account breaks its
EFS usage in post-W2k. For the built-in Adminsitrator account, or
whichever has been set as the default DRA, this can be tragic.