The eth devs are busy working on sharding - the same idea as traditional databases like Mongo where a primary key decides which node the data will reside. The main problem here is that a contract residing on shard A might reference a contract on shard B (much like a join between 2 shards). They are approaching this by using "transaction receipts" that would be passed from shard to shard. https://github.com/ethereum/wiki/wiki/Sharding-FAQ
Indeed - Raiden is all about payment channels - funds are deposited on the main chain and then payments can be sent over channels with no fee. Only in the case of dispute or cashing out is the main chain used to resolve the conflict. This means you could make many transactions per second of very small amounts (useful for things like gambling sites or micro-payments for content). Micro-Raiden is already active which are one-to-one payment channels - the full Raiden network is not yet live but will facilitate one-to-many channels.
