Yeah, simple data layer must be one of the key points. Its basically just rows with a number of columns, stored in either Xml or SQL Database. It makes reading and writing super fast, and forces the developers to decompose their datatypes into simple types that doesn't have any implicit relations which you can risk loading up a deep graph. Something that is easy to do with ie. Entity Framework and then kill performance.
The simple data structure also makes C1 a good candidate for using NoSql document databases like MongoDB, which makes scale out really easy.
Performance Profiling is a first class citizen as mawtex mentions, and its easy to keep track of all stages of a request, background compiling etc. and find bottlenecks as they appear. Running C1 under .Net 4.5 on a multi core machine have also shown a clear performance boosts due to the highly multi threaded nature of C1 and how ASP.Net in .Net 4.5 finally seems to have come up to speed.
The simple data structure also makes C1 a good candidate for using NoSql document databases like MongoDB, which makes scale out really easy.
Performance Profiling is a first class citizen as mawtex mentions, and its easy to keep track of all stages of a request, background compiling etc. and find bottlenecks as they appear. Running C1 under .Net 4.5 on a multi core machine have also shown a clear performance boosts due to the highly multi threaded nature of C1 and how ASP.Net in .Net 4.5 finally seems to have come up to speed.