[Joe]

Obama joined the right church to get where he wanted to get quickly - for a black guy looking to get into Chicago politics, there was no other choice. Yes, the black church is militant and there are some fringe preachers out there.
Now, Obama's aligning himself with another minister for different political ends.
Later, he'll probably align himself with someone else.
Don't kid yourself, Obama prays at the Church of Obama. He sees ministers as minor supporting players in the movie he's starring in.

I read the article.
Political Negatives: Rick Warren delivering the invocation will alienate the far left elements of the Obama camp and anger far right evangelicals - two groups that are intractably aligned with their respective parties.
Positives: Rick Warren's ministry is much more mainstream than any other evangelical since Billy Graham - it contains many moderates. This move shows that Obama is willing to make a gesture to evangelicals, a page from the Bill Clinton playbook.
Opinion: I see it as a wise political move. The people on the right who would never side with Obama because he is pro-choice are never coming anyway, and the people on the far left have nowhere to leave to. Moderate democrats see it as a non-issue.
This move is clearly aimed at creating a relationship with with moderate evangelicals. At the end of the day it will only be marginally successful to that end, but he'll be able to say that he is reaching out.