After nearly 3 years of industry experience in Microsoft technologies, if asked which platform I would personally support for web-application development, I will blindly say PHP.
Some of the reasons

1. Dynamic typed language which 
1. simplifies development & 
2. reduces memory foot print which in turn improves performance.
2. No overhead of rendering server controls to Client Controls.
3. Every major technology in web development like URL routing, HTTP compressions, ETag caching etc; are first implemented on LAMP and later ported to other platforms like JAVA and .NET/MONO.
4. A huge community of open source projects and developers.

PHP is the most widely used web development language in the world. Microsoft is rigorously trying to counter that by introducing new tools and technologies. Razor(view engine for ASP.NET) and WebMatrix is the most recent attempt to lure the PHP developers. “Razor” the new view-engine option in ASP.NET which is optimized around HTML generation using a code-focused templating approach. Web development is frustrating if communication with HTML and JavaScript is difficult as is the case of “Web Forms Architecture”.

Razor provides very simple communication with HTML and JavaScript. The web-development architecture of Razor is very much similar to the basic (traditional FORM based) ASP.NET, except the addition of dynamically typed variable. Razor is easy to learn and enables you to quickly be productive with a minimum of concepts. You use all your existing language and HTML skills.
Unit Testable: The Razor engine implementation will support the ability to unit test views (without requiring a controller or web-server, and can be hosted in any unit test project – no special app-domain required). Not a new language: Razor enables developers to use their existing C#/VB (or other) language skills, and deliver a template markup syntax that enables an awesome HTML construction workflow with your language of choice. Finally, I would also like to talk about WebMatrix. WebMatrix is a free IDE released by Microsoft, that allows developers to build websites using Razor engine. Surprisingly Microsoft also provided support for PHP development. They also claim of improved support for PHP on Windows. After a decade I feel that web-developers might finally find Microsoft more appealing.

Reference:
http://www.microsoft.com/web/webmatrix/
http://www.asp.net/webmatrix/tutorials/2-introduction-to-asp-net-web-programming-using-the-razor-syntax
http://www.microsoft.com/web/platform/phponwindows.aspx