This has been an ongoing issue for around 4-5 months now, maybe more. Nothing special seems to bring up these lock ups, but about every 2-3 games on average more or less at a random point the game will lock up for anywhere between 2 and 20 seconds, the game itself is frozen, but nothing else unless its a long lockup, then everything else will be affected until it ends.
I initially didn't mind because it was random, but the last few times have been right before a team fight so I've officially had it. As far as I'm aware this doesn't happen with most of my other games.
Running: 1st gen i7 950 @ 3.07GHz
I run a standard dual monitor setup each at 1920x1080
Most settings maxed and vsync is off
I typically run a few tabs of Chrome in the background along with steam, skype or vent and media player but I've been able to run a few more things than that and not run into any trouble too.
So I'm stumped. Going to try re-installing the whole game soon even though I don't want it to forget key bindings or anything.