Spiegel has designated Gauck's nomination as "Merkel's biggest defeat"; the FDP supporting SPD/Greens is hailed as "a giant break of trust" by CDU representatives. This includes some major internal CDU people like Bernhard Vogel or Wolfgang Bosbach.
Both Die Linke and the (small remaining) left wing of the SPD under General Secretary Andrea Nahles criticize the nomination of Gauck and the process in which the nomination was handled, excluding Die Linke from cross-partisan talks.
The way this is going i doubt Gauck will garner even just say 900 votes from the 1,099 votes the five parties supporting him hold. High enough to win, low enough to be a Blamage.