Rant Mode On...
Maybe I'm not smart enough - but it really bugs me to download docs and see this in terms of the API:
Include as much detail as possible about your shipment. The RateService WSDL provides elements to identify your shipment, including shipping option elements. This information is important for calculating the correct shipping costs with surcharges.
Well, yeah, sure, the WSDL can tell you how to form your request, but, um, would a table of details have hurt you? This is almost as nice as the Google APIs. I won't say where I found this, but you can probably guess by the quote. Of course, now that I've blogged this, someone will point out to me where the docs are.
Rant Mode Off.