We should all be asking the question: "What do I do if they come and take my server away? My disks? My backup tapes?"
One thing is to know your rights--know how to read a subpoena or a warrant; know your POC in your legal office.
Know what you're going to do next if all else fails and you're left looking at a bunch of dangling network cables...this is where the oft-maligned "cold standby" system can be handy--they're not likely to take a system that's still in a box, or is in a storage room, not connected to your network. It's another reason why you need to have off-site backup--your DR site is not likely to be named in a warrant, and if they don't ask for it, you don't have to "give it up."