From the Freedom From Religion Foundation:

FFRF asks Obama to drop religion in presidential oath
November 9, 2012

The Freedom From Religion Foundation has sent a letter to President Obama asking him to reject the way this country politicizes religion. The Constitution, which prescribes the oath in Art. 2, Sect. 1, does not contain the “so help me God” language or require use of a bible. As FFRF has always done before presidential inaugurations, we are asking President Obama to honor the Constitution on Jan. 21 by omitting that religious verbiage from the Oath of Office.

Secular Americans are the fastest growing religious identification demographic in this country. It’s time politicians stop pandering to the religious right and start courting us.

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Snippets from FFRF's letter:

... 1-in-3 Americans under 30 now identify as nonreligious. This is the demographic that, by a wide margin, elected you in 2008 and again in 2012.... More and more they are tired of leaders injecting religion into politics.

... You are not beholden to any future constituency. This term is a chance to do something that no president in recent memory has done: reach out to secular Americans.... Use this second term to build a legacy by rejecting the way this country politicizes religion.

You can start on January 21. When you stand to reaffirm your oath, do so using the language of the Founders. Eliminate the religious verbiage. While you’re at it, why not place your hand on the Constitution instead of a bible? ...

The “so help me God” tradition violates the Constitution in the act of promising to uphold it. The ritual ... excludes the people that put you into office and runs against the wishes of the people that created your office....

Use this term to create a legacy worthy of the Founders.... Honor the oath as you recite it on January 21 and lead us into the new era you promised four years ago.

(read the whole thing)

The Christian Post quotes Hemant Mehta as not thinking reciting "so help me God" is a big deal in itself. But "every time we let something like this slip, the Religious Right adds it to their giant list of Ways to Trick People Into Thinking We're a Christian Nation. Let's not let the occasion pass without at least posing a challenge."