30 mph speed limit for bikes?

Where did you get this idea from? Genuine question. I've seen this numerous times, along with the "no speedometer" claim, but have no idea where they came from. The highway code says "The 30 mph limit usually applies to all traffic on all roads with street lighting unless signs show otherwise." ( http://www.direct.gov.uk/en/TravelAndTransport/Highwaycode/DG_070304. Rule 124)

Surely "all traffic" does not apply only to motor vehicles. I've looked for specific exemptions in the cycling sections of the highway code, but can't find anything. Does anyone have the relevant section that covers speed limits for bikes, if such a section exists? Similarly, I can find no restriction for bikes at 30mph for all roads, regardless of posted limit. AFAIAA, cycles can legally travel at up to, but not in excess of, the posted speed limit, just like standard cars and motorbikes.
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The Highway Code isn't law itself, it's just summarising the laws and giving some extrea advice. It gives links to the relevant laws which, for speeding (the RTRA), it'll say "motor vehicles". If the Law says "motor vehicles" then it doesn't apply to non-motor vehicles. Google for the text of the law and look it up for yourself.

The latest revisions of the HWC have weasel words of:-

"
Although failure to comply with the other rules of the Code will not, in itself, cause a person to be prosecuted, The Highway Code may be used in evidence in any court proceedings under the Traffic Acts (see 'The road user and the law') to establish liability. This includes rules which use advisory wording such as ‘should/should not’ or ‘do/do not’.
"

MUST and MUST NOT usually mean there's a law. SHOULD or SHOULD NOT just means it's advisory but they may still try and get you.

You're not breaking the Road Traffic Regulation Act 1984 by going over 30mph on a bicycle in a built up area.

Further to this: http://www.bikeforall.net/content/cycling_and_the_law.php

Note the section on Cycling Furiously which, according to the references, doesn't actually exist as an offence.