Roaming has become a popular addition to the metagame strategy, wherein one player does not lane nor jungle, but rather simply moves through the jungle/river to initiate ganks on lanes from level 1 and onward, until the teamfight portion of the game begins.
A roamer essentially guarantees that you're either running a solo lane, or two solo lanes if you have a roamer and a jungler. I've also seen a double roamer game played, though this tends to be less effective as enemies who are wise start playing defensively and reduce the effectiveness of your roamers, which put them behind in both CS and levels.
The qualities of a roamer can vary, but the general requirements are that they are mobile, can do burst damage, and have a strong stun or position altering (push, throw, etc.) ability. Taric, Evelynn and Alistar are all very popular choices for roaming. I've also seen Sion and Blitz play roaming effectively, but they were both out of a lack of a jungle spot on the team and normally suit better in a lane.
This strategy is similar to the "double jungle" mindset in that you get three solo lanes, with the exception that there is extra pressure on getting early kills to succeed. A definite risk vs. reward tossup, as successful roamers will quickly catapult your laners ahead in level / CS as well as demoralize your opponents, but unsuccessful roamers will fall just as far behind due to the lack of their presence in the laning phase.
An "Elo Rating" is a method games, usually Online Multiplayer games, use to separate stronger players from players who aren't as fortunate at the game. Using this method, League of Legends chooses who you will play with when you play the Ranked games with other players. To establish an elo rating, you need to play a few ranked game and after a while, you'll be able to see your rating in your profile and while waiting in some lobbies. League of Legends starts new player off at 1200 Elo. Winning, especially against high-Elo opponents, will increase your own Elo rating. Losing will make it drop. The best League of Legends players approach or surpass the 2000 Elo mark.
Best Answer
Tenacity sources are all unique as far as I'm aware. So they don't stack - building multiple tenacity items is a hugely inefficient use of gold.
Krepo's comment about junglers was probably just noting that the most common way to get double tenacity is Spirit of the Ancient Golem (a jungle item) + Mercury Treads, so junglers are most aware of the fact that double tenacity doesn't work.