In reference to the second irule at this link: http://devcentral.f5.com/wiki/iRules.HTTPRequestThrottle.ashx
IPs in the white list are never throttled.
IPs in the black list are always throttled.
IPs in neither list are throttled only if the send a request to a URI in the RequestLimit_URL datagroups.
These datagroups are maintained by you. They are not updated dynamically.
You do not have to use the IP white/black lists, although you must define them otherwise you get an error.
You should use The RequestLimit_URL list. Otherwise nothing is throttled.
This irule is not CMP compatible as is, this means that if you are on version 9.4 or above and using a bigip appliance with multiple CPUs, your virtual will be handled by only one CPU.
This irule also has old commands which will not survive an upgrade to the latest versions (v10.x or v11.x)
As to the first irule at that link: It is simpler and CMP compatible and will survive an upgrade. I wrote it for those reasons although it is not as feature rich as irule 2.
IRule 1 throttles POSTS only, if you want it to throttle GETs instead, just change the POST to a GET in the if statement.
If you need the features of the 2 irule, let us know, we will try to update it.
HTH.