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

You said,

I heard saying that SharePoint development is very tedious, that the platform cannot be very easily customized, etc.

You have been misinformed about SharePoint. All SharePoint pages are ASP.NET pages. You can customize any of them, either directly, or by using Microsoft Office SharePoint Designer, which is free.

Get started at http://msdn.microsoft.com/en-us/sharepoint/default.aspx.