Fred Phelps is a monster, plain and simple. I don't think that Rick Warren is anywhere in the same ballpark. I actually read "The Purpose Driven Life," and although it was shit, it was harmless shit at worst.
The only issue that I can take with the Rev. is his support of Prop. 8. Regardless of what a person believes individually, for any society to actively deny fundamental associational freedoms to any of its members is anathema, and particularly in the United States it is contrary to the spirit of our nation.
However, I don't think that we should single-out R.W. for fault. He's no fire-brand, and after all, he is an evangelical; it would be inconsistent for him to embrace gay rights, although in my opinion his best alternative is to keep quiet on the issue.