How asp.net and open source relates to each other?
open source is a type of licencing for your application, but it doesnt
relate to development tools

u can use any commercial tools and libs, for open source apps

ASP.NET is a development Framework, not a licensing model. There are many
ASP.NET application that use the open-source approach.  I think you may be
getting hung up on semantics and definitions here.
-- Peter
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Yes, you guys are right.  I do understand the difference between the
development environment and licensing model; I worded my question poorly.

The project I'll be working on is for research.  Most of my content will
be contributed in the form of web parts (or something that can be
quickly converted to such) or mashed (is that a verb?) from the web
through publically available APIs.

Initially, I envisioned my site being built upon SharePoint because it
is a nice foundation for managing web parts and incorporating workflow.

A new idea came up today about creating our app as a portal to a set of
mashed-up public sites and doing as little development as possible.
That seemed like a good idea.

Upon later consideration, I had to ask myself, if we go this route, why
not go all the way and use linux, apache, mysql, javascript,
php/python/ruby/script-lang-dujour.  One clear benefit is having free
reserach replicability (SharePoint is nice but it ain't free).

So, if my end users are all going to access my site via  a web browser,
construct a web page from a web part gallery, which in turn use services
on the web then is there any advantage to purchasing Windows IIS,
SharePoint, Visual Studio, and the intractable number of CALs.

I hope this question is more clear to what I'm looking for.

Thanks for your replies.
bob

Sharepoint is one thing, ASP.NET is another.  I understand your hesitation
to go with Sharepoint because of cost issues.  C# and ASP.NET, on the other
hand are essentially free and something very close to open source these
days.  And Microsoft provides free Express tools of good quality to make
development easy for everyone.

Bob,

check this post

Enabling and managing social networks (for business use) with
Microsoft Office SharePoint Server 2007
http://blogs.msdn.com/sharepoint/archive/2007/10/24/enabling-and-managing-social
-networks-for-business-use-with-microsoft-office-sharepoint-server-2007.aspx

...but in my opinion SharePoint is a wrong tool for a social
networking site. It's a solution to everything, and you woudn't need
CALs for the internet version, but the main benefit of going to
Sharepoint is in the integration with Windows-based intranet
components: AD, Office 2007, Exchange... If you don't have all these
things - it makes no big sense to go with SharePoint, -  because there
is nothing ready out-of-the-box for the internet and you would need to
develop a custom application.