"’Document’ means any substance having any matter expressed or described upon it by marks capable of being read." Stephens Digest of the Law of Evidence, 4th ed., Art. I.
There are many pitfalls in attempting to preserve data yourself (see for example, Daticon, Inc. "Avoiding the Spoliation Trap" Glasser-Daily Journal, SanFrancisco, April 2004), but they boil down to one thing: the ignorance of your client’s IT staff about the legal significance of what they are supposed to be doing. Often lawyers think that just because IT staff are technical wizards they should know how to preserve data properly. Well, the preservation of electronic evidence is NOT part of the IT person’s day job, and without a combination of detailed instructions, legal overview, supervision and research, problems arise down the road.