My predictions:
Stan Smith group
1) Djokovic 3-0
2) Federer 2-1
3) Berdych 1-2
4) Nishikori 0-3
Ilie Nastase group
1) Murray 2-1
2) Wawrinka 2-1
3) Nadal 1-2
4) Ferrer 1-2
Semifinals
Djokovic d. Wawrinka 6-3, 7-6
Federer d. Murray 6-3, 6-3
Final
Federer d. Djokovic 7-5, 1-6, 7-5
Comments
Hopefully this even will be better than last year's dreadful edition, when every match was an annihilation until the semi between Federer and Wawrinka, and the crackerjack final between Federer and Djokovic never happened due to Fed's back injury.
I will be shocked if the final is not those two guys again this year. Neither Berdych nor an injured Nishikori will trouble either of them, and whoever emerges as the champion from the other group will be vulnerable: Murray because his mind will be on Davis Cup, Wawrinka because he simply has not played that well since the French Open, Nadal because it's the year-end indoor event and Ferrer because he's Ferrer.