Gloredhel, you're probably right that if the Supreme Court held the "under God" in the pledge to violate the "establishment" Clause, they'd have to apply the same logic to the currency, etc.  [Though you could argue that having kids recite the pledge calls for their active endorsement of the concept of God, whereas passing money does not.]
As a practical matter, of course, it would cost nothing to stop saying prayers in government sessions or having "under God" in the pledge of allegiance and relatively little to notify schools and government officials of the decision.   Changing the US money could cost a great deal.
As for the Declaration of Independence, it's a historical document that has no legal status in the way the Constitution does, so it wouldn't need to be changed.  And does the Constitution mention God?  Where?

Little Hawk, I fear that "bozos" like this guy who brought the suit over "under God" are doing more harm than good to the cause of keeping government and religion separate.  The ones like the late Madeline Murray O'Hare who keep suing every time a school mentions anything Judeo-Christian or a church group wants to hold an Easter service on otherwise-unused public land, etc., just fuel the fires of the far Right, who would like nothing better than to impose much of their religious/moral viewpoint on everyone else.

The Religious Right shouldn't get to holier-than-thou about this sort of intolerance, though.  I've heard many of them objecting to public schools' teaching such things as relaxation skills, "because these techniques have their foundation in transcendental meditation, which is based on Buddhism or other non-Christian beliefs."

Liland, thanks for the link to the history of the pledge.  Wonder how many in the Religious Right know the pledge was written by a minister who did not feel it necessary/appropriate to include "under God" in "what is Caesar's"--or that the author was a (Gasp!) socialist!
And the idea of a church that looks like the EMP--now that's a trip!

Guest Browning (who won't read this if you've really exited), I, for one, am not anti-Christian.  Like a number of Christians, some of whom are Mudcatters, I feel it verges on blasphemy to tie Christianity to capitalism, vengeful militarism, intolerance, eye-for-an-eye "justice," etc., the way the Religious Right in the US tends to do.  Jesus said to give Caesar what is Caesar's and give God what is God's.

Genie (still without my biscuit)