I found two minor bugs, otherwise spectator mode looks cool.
1) Nothing after game completion
Joining a game in progress via the game client home page lobby button, I watched a game through completion. After watching one team claim victory by exploding a Nexus, the game shows "victory" like normal, but I was neither returned back to the game client home page, nor was I presented a game summary screen. I had to terminate LoL and relaunch.
2) Camera lock and Fog of War
If you enable Fog of War for one team, and attempt to camera follow an unseen enemy, the camera defaults to manual (my previous camera setting if that matters)
HOWEVER, if you switch back Fog of War to the opposing team and attempt to follow the same champion, the camera will move to the champion but fail to LOCK the camera. Again, the camera continues on manual. This is fixed by merely switching to another champion and back again, where the camera will then lock on target.