The Debian wiki ignores the HTTP If-Modified-Since header and returns
the full page whether or not it has been modified since the page was
requested. As you can see below, www.d.o (which is based on static
files) works fine. This appears to be a bug in moinmoin since moinmo.in
also has the same issue.

pabs@chianamo ~ $ curl -vso foo --time-cond foo wiki.debian.org
* About to connect() to wiki.debian.org port 80 (#0)
*   Trying 93.94.130.161...
* connected
* Connected to wiki.debian.org (93.94.130.161) port 80 (#0)
* additional stuff not fine transfer.c:1037: 0 0
* HTTP 1.1 or later with persistent connection, pipelining supported
< HTTP/1.1 200 OK
< Date: Fri, 10 Aug 2012 22:19:56 GMT
< Server: Apache
< Vary: Cookie,User-Agent,Accept-Language,Accept-Encoding
< Transfer-Encoding: chunked
< Content-Type: text/html; charset=utf-8
<
{ [data not shown]
* Connection #0 to host wiki.debian.org left intact
* Closing connection #0
pabs@chianamo ~ $ curl -vso foo --time-cond foo wiki.debian.org
* About to connect() to wiki.debian.org port 80 (#0)
*   Trying 93.94.130.161...
* connected
* Connected to wiki.debian.org (93.94.130.161) port 80 (#0)
* additional stuff not fine transfer.c:1037: 0 0
* HTTP 1.1 or later with persistent connection, pipelining supported
< HTTP/1.1 200 OK
< Date: Fri, 10 Aug 2012 22:20:05 GMT
< Server: Apache
< Vary: Cookie,User-Agent,Accept-Language,Accept-Encoding
< Transfer-Encoding: chunked
< Content-Type: text/html; charset=utf-8
<
{ [data not shown]
* Connection #0 to host wiki.debian.org left intact
* Closing connection #0
pabs@chianamo ~ $ rm -f foo
pabs@chianamo ~ $ curl -vso foo --time-cond foo www.debian.org
* About to connect() to www.debian.org port 80 (#0)
*   Trying 150.203.164.38...
* connected
* Connected to www.debian.org (150.203.164.38) port 80 (#0)
* additional stuff not fine transfer.c:1037: 0 0
* HTTP 1.1 or later with persistent connection, pipelining supported
< HTTP/1.1 200 OK
< Date: Fri, 10 Aug 2012 22:33:50 GMT
< Server: Apache
< Content-Location: index.en.html
< Vary: negotiate,accept-language,Accept-Encoding
< TCN: choice
< Last-Modified: Thu, 09 Aug 2012 19:28:15 GMT
< ETag: "37f6-4c6da3a9731c0"
< Accept-Ranges: bytes
< Content-Length: 14326
< Cache-Control: max-age=86400
< Expires: Sat, 11 Aug 2012 22:33:50 GMT
< Content-Type: text/html
< Content-Language: en
<
{ [data not shown]
* Connection #0 to host www.debian.org left intact
* Closing connection #0
pabs@chianamo ~ $ curl -vso foo --time-cond foo www.debian.org
* About to connect() to www.debian.org port 80 (#0)
*   Trying 150.203.164.38...
* connected
* Connected to www.debian.org (150.203.164.38) port 80 (#0)
* additional stuff not fine transfer.c:1037: 0 0
* HTTP 1.1 or later with persistent connection, pipelining supported
< HTTP/1.1 304 Not Modified
< Date: Fri, 10 Aug 2012 22:33:54 GMT
< Server: Apache
< ETag: "37f6-4c6da3a9731c0"
< Content-Location: index.en.html
< Expires: Sat, 11 Aug 2012 22:33:54 GMT
< Cache-Control: max-age=86400
< Vary: negotiate,accept-language,Accept-Encoding
<
* Connection #0 to host www.debian.org left intact
* Closing connection #0

TTBOMK servers don't need to do anything special to "support"
If-Modified-Since; IOW they are okay to just send you the document
anyway.

Given you claim this is a bug in moinmoin, we don't need a tracking
bug for this against wiki.d.o. Whenever the wiki is migrated to some
newer software, this can be revisited, _if_ it turns out to be an
actual problem.

Closing for now.

C.