At Obama's inauguration, Rick Warren gave a prayer. I've heard a few Christians up in arms about the prayer, and they generally focus on three things:
1) It was pretty empty.
This is a legitimate criticism. There wasn't much substance to the prayer, and some of the time was spent on "preaching to the choir." On the other hand, one shouldn't expect a prayer to be a sermon. I'm not trying to defend Rick Warren, but I think that some people's expectations would not have been met unless Warren had given a 30 minute prayer-homily.
2) Warren referred to God using this sentence: "And you are the compassionate and merciful one."
The criticism is that this sounds like it is taken from the Koran. It does sound like that. On the other hand, the true God is merciful and compassionate. Scriptures say so. It is not wrong for us to describe God that way, and it may be valuable for Muslims to see that the true God is merciful and compassionate - that such a teaching is not uniquely Koranic, but is borrowed from Christianity.
Psalm 145:8 The LORD is gracious, and full of compassion; slow to anger, and of great mercy.
Psalm 86:15 But thou, O Lord, art a God full of compassion, and gracious, longsuffering, and plenteous in mercy and truth.
3) Warren referred to Jesus as "Isa."
The criticism is, again, that this sounds like it is taken from the Koran. It does sound like that, and if context is not provided, it sounds very suspicious, particularly when coupled with (2) above. In context, however, Warren's sentence was:
"I humbly ask this in the name of the one who changed my life, Yeshua, Isa, Jesus [Spanish pronunciation], Jesus, who taught us to pray: [full length version of Lord's Prayer]."
In context, Warren was simply giving the Arabic name for Jesus in a list among the Hebrew name, the Spanish name, and the English name. In context, Warren is positively affirming that Jesus taught his disciples to pray like Christians, not like Muslims - although he is using the name for Jesus that is familiar to Muslims.
I am not a fan of Rick Warren, and I am not praising his prayer. The fact that he prayed in Jesus' name is great, but that's sort of a minimal bar. There are many ways his prayer could have been improved. On the other hand, I don't think that the claims that Warren was trying to be "ecumenical with Muslims" is valid - or at least cannot be shown from his prayer.
Now, I am not familiar with a large body of what Warren has said elsewhere. So, perhaps, viewed in light of the remainder of what he has said, these seemingly reasonable references could be viewed as inappropriate concessions. No one that I have seen criticize Warren, however, has brought forth that kind of evidence.