Since I  am tired to answer questions related to identites confusion in many posts
I decided to separate it in dedicated post.

 User.Identity.Name represents identity passed from IIS.

WindowsIdentity.GetCurrent().Name is he identity under which the thread is running.

Now their values are:

=============================================================================
Impersonate attribute          Anonymous     User.Identity.Name      WindowsIdentity.GetCurrent().Name
(web.config  in <identity>     access (in IIS)  (id passed from IIS)      (thread's identity)
----------------------------------------------------------------------------------------------------------------------------------------
"true"                                   Yes                    Empty string                 IUSR_<machineName>

"false"                                   Yes                   Empty string                 NT Authority\Network Service(*)

"true"                                    No                    domain\user(**)           domain\user(**)         

"false"                                   No                    domain\user(**)           NT Authority\Network Service(*)

==============================================================================

(*) - NT Authority\Network Service (for server Windows) or ASPNET (machineName\ASPNET_WP (for Windows XP)

(**) - domain\user (for AD) or machineName\userName (for local account)

Hi,

you can post that thread here in FAQ section

http://forums.asp.net/13.aspx 

Satalaj

Or

you can bookmark this already nice little article:

http://www.bluevisionsoftware.com/WebSite/TipsAndTricksDetails.aspx?Name=AspNetAccount 

Better this one
http://msdn.microsoft.com/en-us/library/aa302377.aspx

Nice one. Thanks for sharing.

Well, my starting post was moved to FAQ before I finished editing it.
And I could not  edit it since.

Though it contains inaccuracies...


Though I feel better by the fact that cited articles contain even bigger errors...