You should go check that you created the zone correctly in dns.he.net if that is what you used in order to list HE name servers.

This was it! It's working fine now. I was originally using the godaddy name servers, but changed over to HE after finding out that godaddy doesn't support reverse DNS. Thought I had already added the AAAA record under dns.he.net, but apparently not, as I discovered when I double-checked today... This is what I get for trying to set this up at 1:00am, with insufficient quantities of caffeine 
Thanks for the extra set of eyes and for putting up with a noob...

Thanks for the feedback everyone, I really appreciate it!
I should have done this before, but I just did an nslookup using HE's name servers, and they still don't seem to know about my domain:

>nslookup dostiedemo.info ns2.he.net
Server: ns2.he.net
Address: 216.66.80.18

***No internal type for both IPv4 and IPv6 Addresses (A+AAAA) records available for dostiedemo.info

Google and other public DNS servers do return the quad-A record. Does it usually take a long time for HE's name servers to catch up? Should I transfer my DNS records to HE's name servers?

As to the tunnel broker, I only used gogo6 because it was the first one I came across awhile back and it hasn't given me any problems, but I can certainly give it a try using HE's service.

Hi all,
Not sure what I am doing wrong, but I cannot get the Enthusiast test work properly.

1. I registered a domain name at godaddy.com: dostiedemo.info
2. I created a AAAA record to point to the local endpoint address of my tunnel: 2001:5c0:1000:a::d07 (I used the gogo6 client to create the tunnel)
3. I set up an IIS web server and placed a file named dydrh6atcb.txt in the wwwroot folder.
4. I can access the full URL - http://dostiedemo.info/dydrh6atcb.txt - and I can also access the site via its IPv6 address from outside my local network.

Yet, the test keeps returning the same error:

Could not grab the file via IPv6 HTTP
[Reset Test]
Help   Step   Description   Data
   [1]   Completed: Code generated    dydrh6atcb
   [2]   Completed: Valid FQDN entered    http://dostiedemo.info /
   [3]   Completed: URL created:    http://dostiedemo.info/dydrh6atcb.txt

Any suggestions or ideas to try would be appreciated!
Thanks!