Developing a website for 3 mln. users: SharePoint OR pure ASP.NET?

Question

We need to develop quite a powerful web application for an investment bank. The bank IT would like us to build it on top of the SharePoint platform

Answer 1

This is a matter of what kind of concerns you want to have in the application:

• Building it to look and function your way, go with sharepoint.
• Building it to have infrastructure for authentication, permissions, http/web security, scalability, backup, database maintenance PLUS getting it to look and function your way (but now way more under your control), go with a more pure .NET approach.

I would pick the one I am best at, as Kevin said above.

Edit
More about Kevins post: you can also have your application under sharepoint but with full access to the API, in my projects we do it as a normal ASP.NET application, with own masterpages and everything, but we still use the authentication, lists and doc libraries for uploads, roleassignments for permissions etc. Its a very viable hybrid.