After learning how SPNs work (read my "Who? Why? Where" to learn what's an SPN), I was frustrated to find out that I can't implement my experience in the real world.
I've created a Sharepoint Central Admin site on port 1234, and wanted to enable kerberos authentication for it, so I've created an SPN reading http/server:1234 on the right account, and it didn't work!
The SPN that did work is http/server, which should work only for the site on port 80 (because it's the default port for HTTP). Turns out that IE6 had a bug, which caused it to always request TGS without port numbers (http/server), even when navigating to a site in a non-default port. A hotfix (kb908209) was issued and all was well. Problem is, we use IE8! Surely, someone must have fixed that behavior in the new browsers?
Apparently, in order to maintain compatibility, new versions of IE(7+) use the same defected SPN formulation. To switch to the new version, you have to add this registry key:

  • x86:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_INCLUDE_PORT_IN_SPN_KB908209:iexplore.exe=1
  • x64:

    HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_INCLUDE_PORT_IN_SPN_KB908209:iexplore.exe=1

I used Group Policy Preferences to distribute it to all my servers.