It has been cited often that on Summoners' Rift ranked solo queue, blue side wins around 55% of the time. The effect of the "blue side advantage" is so great that it is often said that Riot puts slightly higher elo teams on the purple side in an attempt to balance out the map advantage by simply spawning on the blue side.
I have been interested in this in a while, but as far as Summoners' Rift is concerned, there are several factors one needs to consider:
1. Spawning position of jungle monsters.
2. Dragon/Baron lay out.
3. Pick order (in ranked).
4. Camera angle.
With the introduction of One For All Mirror Mode on the ARAM map, it creates an unique situation which:
1. No jungle.
2. No Dragon/Baron.
3. It's the same champion times 10.
But the camera angle remains. So on this map we actually remove a lot of the other factors which may make the blue side stronger. With this in mind, I quickly found ~3500 games played on this new game mode during the last 4 hours or so. I got the following:
Blue side won: 1946 games
Blue side lost: 1505 games
So overall, blue side wins 56.4% on One For All Mirror Mode. This estimate is accurate within plus or minus 1.6%, 19 times out of 20. This is very similar to the blue side win rate on ARAM maps in general, which is around 56%.
In comparison, on Twisted Treeline where the map is totally symmetric and camera angel is not an issue, the blue side (left side) wins exactly 50% of the time.
So, it does look to me that there is an effect from camera angle that makes the blue side stronger on Summoners' Rift and on ARAM map. I wonder what the consequence is, especially on the competitive scene. It almost feels to me that playing on the blue side is sort of like playing as white on chess - while the advantage is not as big as white side on chess, the advantage is certainly there and it's real.