Arguably one of the main aspects of League of Legends which is holding it back competitively is the need for a spectator and replay mode.

Riot are addressing the first issue and spectator mode is imminent, apparently we will see it in the next month or so but replay mode will come much later.

We do have some preliminary details on the spectator mode. The spectator will join prior to game start and will be able to chat with the players in the lobby. In addition the spectator will see all aspects of the draft and banning phase.

Once the game starts, the spec won't be able to chat or see the chat of the teams, in addition there is set to be a 15-30 second delay to prevent ghosting, however in my opinion this isn't nearly enough. As shown from livestreams, a delay of around 4 minutes is typically agreed, this is influenced by wards lasting 3 minutes.

The spectator gets a totally new UI while in game, it has counters for things such as team gold acquired, team kills and both team portraits on the side of the screen, this allows for the spec to quickly jump to each champion.

As shown in tournament casts, there is also the ability to toggle the Fog of War on or off.

Riot haven't stated yet whether or not there will be a limit to the number of spectators but they have said that players will be able to set whether or not they wish to be spec'd and will have the option to kick specs.

Just a note, Riot have said that replay mode will come but not in the next month or so.