I thought I heard something about the President being on tonight.

Does anyone know for sure if Survivor will be on at 8:00 pm ?

Yes. On the CBS site it says Survivor will air right after the press conference.

The President's press conference is scheduled for 8pm Eastern time... Last I heard... So yes, it'll muck up the primetime schedule for some areas. How they'll handle it is pretty impossible to predict.

edit: see Gandalf's note... It makes sense that they're gonna broadcast S3 in the best slot they've got left...