Formula Run-Time Performance

Formulas specified at development time are saved as strings and evaluated in the code-behind during the initial display or postback of a page.  The formula is not evaluated in JavaScript or any client-side script; instead it is only evaluated on the server-side.  The formula editor first parses the formula and then evaluates it.  Formula parsing is based on a simple grammar and is extremely fast.  The actual formula evaluation is then performed by generating Common Intermediate Language (CIL).  CIL is the compiled language that all C# and Visual Basic .NET are converted into prior to execution, so formula evaluation is as fast as compiled C# or Visual Basic .NET.  The only overhead comes from the parsing the formula, and this is minimal because of the simple nature of the formula.

Reference

http://en.wikipedia.org/wiki/Common_Intermediate_Language

From Wikipedia:  Common Intermediate Language (formerly called Microsoft Intermediate Language or MSIL) is the lowest-level human-readable programming language defined by the Common Language Infrastructure specification and used by the .NET Framework.