• In which format do the spikes occur: 3v3, 5v5, ARAM, unranked, ranked, etc?
I generally only play 3v3, so I can't really say if the spikes happen in the other games modes.
• Does it happen at a particular time/location: during team fights, when you’re at spawn, randomly, etc?
Happens at random.
• How often are the spikes?
Again, at random intervals. Sometimes I'll go an entire game without a spike, sometimes I'll get a spike ten minutes in, sometimes, I won't even be able to get into the game because of it.
• How long do they last?
Anywhere between two and ten minutes.
• What symptom(s) do you see during spikes: champion “ice-skating” or jumping around, game hitches, etc?
My champion will react to any command I give, however, I can't see any opposing champion movement. I can only see my own teams movements. I can watch health bars drop, with no idea as to where the enemy is. Minions will freeze in place momentarily, and then begin to slide from where they stopped to where I assume they have moved to, appearing to still be targetting whatever it was they were last targetting, wherever that has moved to.
• What’s your ISP?
AT&T in Monterey, CA
• Do the spikes only happen in LoL?
Yes.

1.Any game type
2. Usually tends to happen right before a teamfight and/or during it...sometimes it's random
3. After every minute or so. sometimes even after a couple of seconds.
4. a couple seconds, sometimes even 30 seconds upto a minute sometimes
5. Just jumping around, or staying in one place. sometimes i would see other's health bar dropping, including mine, i see minion shots everywhere, and suddenly either i end up in a whole another place, or dead.
6.Only happens in LoL

There was a fix I found in another thread for a similar(?) problem.
Here. All you really have to do is delete your entire lol_air_client folder and repatch from the beginning. It's time consuming, but I did it and I'm not having problems anymore.

bump, still having this damn lag.

1. Any game type -- So far I've been playing ranked.
2. Randomly.
3. Usually within seconds.
4. They last a long time; Sometimes seconds to minutes.
5. I'll see ice-skating -- Mostly jumping around for the most part. I'm not sure what game hitches mean but usually I'll stay in one spot for the longest time \:
6. Netgear
7. Yes :c

Just got out of a game, got disconnected from internet and got a leave/loss, even though we were winning.

1. So far I've only been playing 5v5
2. Usually straight after something happens; i.e fight initiates
3. 2-4 times pre minute
3. 2-3 seconds
4. Everything stops, then 3 seconds later everything jumps to its current location.
The spikes only happen in LoL.

Also, I would like to add that when the game acts like this the leagueoflegends.exe process is taking around 1Gb RAM; even up to 1.5Gb at times; whereas it used to take up to like 700Mb tops.

Having these problems too. As stated, it's making the game unplayable. Weird thing is that it doesn't happen to my friends; I'm the unfortunate one.