I haven't read this book myself, but I saw over someone's shoulder yesterday that in The Purpose Driven Life Rick Warren writes this:
You have heard people say, "I can't make it to the meeting tonight, but I'll be with you in spirit." Do you know what that means? Nothing, it's worthless! As long as you're on earth, your spirit can only be where your body is. If your body isn't there then neither are you. (p105)Which makes me wonder what Rick would make of 2 Kings 5, where Elisha's heart/spirit (לִבִּ֣י) follows Gehazi as he commits his crime and so consequently is cursed with leprosy. Or more pertinently, of Paul in 1 Cor 5:4 where says he will be with the Corinthians in spirit (πνεύματος) when they assemble to deal with the incestuous man. Of course Elisha did not mean that he was there but only that he was aware of what was happening (Elisha could work out the intentions of enemy kings from a distance, so his own bumbling servant would not pose much problem) and Paul did not mean he was there except by the fact that the Corinthians knew his decision on the matter and he wanted them to behave as if he was there giving his full apostolic weight to his opinion. I'm sure most people who use the expression "with you in spirit" do not mean that they will actually be there, but instead mean that they will be thinking of you and praying for you and want you to know and feel their support in that time. Which is nothing like worthless at all.