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So recently, I was suffering from extreme lag, bugged up keyboard issues, and a client that was incredibly prone to crashing. I deleted League from my computer, then proceeded to redownload and install the newest version. Everything was fixed.
I'm inclined to believe at the moment that many of the issues people are suffering might be due to an issue during the update where some out of date coding didn't get properly overwritten or something.
If you haven't tried reinstalling the game yet, I'd give it a shot. My copy of LoL used to be unplayable, and now it works fine.