First of all, I believe League of Legends has the potential be a phenomenal game in the competitive scene within the next 2 years. I mean probably up there next to starcraft and Counter-strike. I can't think of any other competitive game that is as reliant on teamwork and precise coordination and much as much fun. Sure there are some imbalances and bugs and the state of the game has been quite volatile initially, but that all improves over time. If anything is going to hold back League of Legends from being run in pro circuits, it is the lack of an LAN and easily deployable game client.
With this said, I am concerned about how the grass-roots growth of the competitive scene is going to play out. This has mostly to do with the lack of LAN multiplayer. From my understanding, this game is based on a Server-Client model where the server is controlled by Riot. Where I live, we could never have a major tournament because of the ping delay of playing on servers hosted across the ocean. In very highly competitive play, 80+ ping delay can impose a huge impact on professional level games. Major tournaments and events sponsored by pro-gaming circuits probably won't roll over very well when Team X just gets annihilated because of a lag spike from the Riot Servers. International tournaments will have the hardest hit from this as well.
Also, the dependence on Adobe Air as a platform creates really high costs of deployment on many systems and most rapid software deployment methods will not work with AIR. For the second time in a row, I was unable to host League of Legends at a major annual university lan-party because of this. I'm sure many other local grass-roots driven events will suffer the same constraints.
If there was a LAN/Offline client that users could host games locally for optimal competitive play at LAN tournaments, as well as a portable distribution of AIR that allowed the game client to be deployed across many systems this would solve these issues and will help the growth of flourishing competitive League of Legends scenes.