Microsoft has always put limitations for licensing purposes on SQL Server. Express edition could only use 2GB of RAM. Standard edition was a laggard in terms of features in Analysis Services. Most of the time this required our customers to purchase Enterprise edition, and possibly sacrifice a scale-out architecture for scaling-up.
Scale-up might not let you get around these limitations with SQL 2008 R2. Datacenter edition might be the only option for those customers with > 8 CPUs.
What is new for SQL Server 2008 R2 Standard Edition and SQL Server 2008 R2 Enterprise Edition, are more restrictive hardware license limits compared to the SQL Server 2008 versions of both of those editions.
SQL Server 2008 Enterprise Edition had no limit for the number of processor sockets, but was limited to 64 logical processors. SQL Server 2008 R2 Enterprise Edition imposes a new limit of eight physical processor sockets, but will theoretically let you use up to 256 logical processors (as long as you are running on Windows Server 2008 R2). However, this is not possible, currently, since it would require a processor with 32 logical cores. As of April 2011, the highest logical core count you can get in a single processor socket is 20 (if you are using the new Intel Xeon E7 series). Also, the RAM limit for R2 has changed from “operating system limit”, as it was in the 2008 release, to a hard limit of 2TB.
SQL Server 2008 R2 Standard Edition has a new RAM limit of 64GB. This lowered limit may catch many people by surprise, since it is very easy to have much more than 64GB of RAM, even in a two-socket server. You should keep this RAM limit in mind if you are buying a new server and you know that you will be using Standard Edition. One possible workaround for this limit would be to have a second or third instance of SQL Server 2008 R2 Standard Edition installed on the same machine, so you could use more than the 64GB limit for a single instance. The physical socket limit for SQL Server 2008 R2 Standard Edition is still four processor sockets.