If you happen to be MSDN subscriber, there is new treat for you. SQL Server 2012 is available for download.
For those as cheap as me, there is SQL Server 2012 Express. For some reason it is still listed as beta, but I expect to see RTM version soon enough.
Biggest feature in my book would be LocalDB. On first glance it would be same thing as SQL Server Compact. However, if you dig a bit deeper, you will see that it has few subtle differences.
For me LocalDB is missing link that brings SQL Server data and TSQL without need for full-blown SQL Server install. Compared to Compact, it is bigger and not as easily distributed. On other hand, upgrade between LocalDB and full SQL Server should be a breeze. This one goes on my system immediately. Check more details.
Yes, there are other changes, but I will leave each one of you to pick a favorite.