Just a quick observation without the science to back it up but Snort alerts on it..... You don;'t make Snort rules for something that is utterly harmless..... If I remember I'll go look and see why.

[Edit]

You know, sometimes, good questions are more valuable than good answers.... Nice one Slarty.....

[/Edit]

[re-Edit]

Looks like there are a couple of things out there. Zero is a reserved port as stated and demonstrated in this link. The RFC, (1700), refered to in that document confirms that port zero is reserved.

The interesting part about the document is the OS fingerprinting part that PM(?) mentioned. and thus the reason for the Snort rules.

And as I mentioned above about good questions being better then good answers sometimes I found out and answer as to why my Win2k box scanned by SecuritySpace and others keeps coming up as a Linux box......

Unfortunalty both MS Windows 2000 and Linux have the same port 0 fingerprint, relpying to all 7 tests.
That's why good questions are sometimes better then good answers.... They can lead to the answers to other questions......

[/re_Edit]