Fred Wilson has a good post on how to balance life and vacation. I find it impossible to completely unplug from work during vacation. I suffer some kind of anxiety attack if I don't check email at least every 24 hours (more like every 2 hours during waking hours).
Step 1: Give up all hope of remaining unconnected. The earlier you give up, the better you'll feel.
Step 2: Change your voice mail greeting and tell people to not even bother leaving messages. Optionally leave your email address on your message so that you can handle things asynchronously.
Step 3: Keep your cell phone off. I once blew 2 hours negotiating a merger on my cell phone that in hind sight we probably shouldn't have done. I could have, and should have, skipped the call. If your team and coworkers can't handle any fires that come up, they'll figure it out. People actually lived without cell phones once.
Step 4: As Fred said, all family events get priority.
Step 5: Scan email infrequently and respond to as few things as possible. You don't want to get into email conversations.
Step 6: Make sure you have an understanding spouse or ignore all of above.