Enterprise class framework and tools.

You can knock Microsoft all you want, I do, but .Net and C# are great. And have you opened Visual Studio 2010... I'ts the best IDE out hands down.

Free as in beer...for three years.

Microsoft Bizspark offers a variety of different programs for startups. You can get the software you need, the hosting you need, and even introductions you need. That is if you meet the requirements, but I would bet a lot do.

I know it.

Therefor my ramp up time will be less than if I were to use something like PHP. One of the driving factors in startups is speed... Especially in a competitive market. 

Title: O'Reilly Webcast: How to Build a Lean Startup, Step by Step
Presenter: Eric Ries
Runtime: 1 Hour 6 Minutes
Publisher: O'Reilly Media
Publish Date: May 02, 2009

About:
Get started with a detailed guide to three key lean startup techniques: continuous deployment, rapid split-testing, and root cause analysis (five why's). In this webcast, Eric Ries, author of the blog StartupLessonsLearned, covers the theory of how lean startups work, implementation details, and case studies. Participants will come away with a specific plan of action for how to apply these techniques to their product, company, or startup.