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.
You need Lifesteal. A "getaway" technique, for example Talon, can easily use his E or even his ult to dash away. Teemo can also use his speed.
Best Answer
There are a few reasons to swap lanes.
One thing to remember if you're going to send your adc/sup top is that if they cant get the tower down, and get back bottom lane by 4-5ish you're risking a dragon to the opponent (their adc/support is still bottom and able to help with dragon while yours is on the other side of the map).
Another important note, as of patch 4.1, top and mid turrets gained 20 damage reduction from champion basic attacks. This makes lane swapping even more risky as the duo that goes bottom won't have this damage reduction to deal with.