Microsoft announced SQL Server 2014 at the 2013 North American TechEd conference in New Orleans yesterday, with a Community Technology Preview (CPT) to be released "within a few weeks"
One of the features we at MyDBA are excited about in SQL 2014 is "In-Memory OLTP", a feature that allows OLTP tables to be defined as in-memory tables rather than regular "on disk" tables. 
In-memory tables will optimise performance through 4 key mechanisms:
  • Elimination of disk reads entirely by always residing in memory
  • Hash indexing (more efficient than on-disk table b-tree indexes)
  • Elimination of locking & latching mechanisms used in on-disk tables
  • Reduction in "blocking" via improved multi-version concurrency model
Instead of being an entirely new form of in-memory database engine, SQL Server 2014's In-Memory OLTP is a feature available within any SQL Server database, allowing you to configure specific existing or new tables as "in-memory" or have a mixture of "in-memory" and "on-disk" tables.
This approach is a significant innovation from Microsoft, making In-Memory technology more readily accessible than having to migrate to an entirely new database engine, as is required with most other in memory database solutions
There are some limits to which tables can be configured as "in-memory" but we think that the limitations are reasonable and will still allow wide spread use of this feature.
Tables containing binary columns such as text, xml or row width exceeding 8kB cannot be configured as "in-memory" and there are also some limits on SQL commands and transaction concurrency options. 
Despite these limitations we think In-Memory OLTP will be the one of the most important database engine optimisations since SQL 2008 introduced database compression.
Microsoft have also published a YouTube video on the benefits one of the largest SQL Server implementations in the world (BWin) has already realised from using SQL 2014 In-Memory OLTP technology.
Implementing SQL 2014's In-memory OLTP technology in their web session state database server, BWin's peak transaction rate increased from 15,000 tx p/sec to 250,000 tx p/sec.
Whilst SQL 2014 won't be released until next year, we are excited about "In-Memory OLTP" and already thinking ahead about how our customers will be able to reach new performance levels, not thinkable with existing SQL 2012 technology.
Imagine... a future without disk bottlenecks, locking, blocking or deadlocks!