This is a long reply because I've been doing a lot of testing, but I've underlined the most relevant information to help keep this organized.  Thank you for help.

Well, I have setup a HTML module to display only for those who aren't authenticated and it has a link to a page that logs their IP Address, username and IE Version before redirecting them to the WindowsSignin page.  I've noticed that people are getting errors with IE 6 and 7.  I've also noticed that it's not just that 30 users like I had originally thought, but that it seems to sporadically change who's affected.  Local administrators experience issues as well.  I've also noticed that everytime there's a failure, the username get's logged correctly, so it appears that at least IIS is seeing the user who's logged in correctly.

Some additional information regarding IIS and client configuration: the website is hosted using a DNS alias, and we have registered SPNs for that alias using the SETSPN command.  Also, we have "Enable Integrated Windows Authentication" checked on all computers, and all computers have the following registry key added from another problem that we've had in the past: [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_USE_CNAME_FOR_SPN_KB911149]
"Iexplore.exe"=dword:00000001

All users have the same version on AV installed, and group policy controls the windows firewall settings.  Unauthorized applications cannot be installed except by administrators, and there aren't many.  The users who are experiencing the issues do not appear to have any unique characteristics, and everyday a different group of people is affected, but some users appear more than once, and a couple seem to have to log in more than once in the span of a few minutes.

That's an interesting thought, it's possible, but how would I be able to tell which domain controller it might be authenticating to.  Also, is there a way to override it to look at just one server?

Also, it seems that they are able to manually login by navigating to the windowssignin.aspx page (although sometimes it takes a little longer than expected for some users).  Would that fact negate the possibility of problem at the authenticating server, or does it use a different means than the automatic login?

I've been having issues with people in various locations who authenticate to different DCs.  We have them setup to always use the DC closest to them.  I Maybe IIS (and not the client) is authenticating to different servers to authenticate on behalf of the client, perhaps that's in line with your theory.

I'm working with our Systems Administrator to see if I can get an export of all the AD and FRS logs and perhaps find an error somewhere.  The confusing thing is that even in my location, there are people who have received the issue.  But I myself never have.  And some get it everyday, but others once or twice a week.  Some (like myself) never see the error.

Hopefully the logs give me some insight, I will respond to this forum with the results.  Thanks for your assistance thus far.