Microsoft has released a patch for Vista that cures several problems with USB devices, including devices that hang when resuming from Sleep. Here's the solution:
Reliability update for the USB stack in Windows Vista
Finding this patch isn't particularly easy if Google is your only search engine. The knowledgebase article doesn't mention ReadyBoost at all. It comes up as the first result if you search support.microsoft.com for vista and usb, but it's on page three if you search Google for vista usb hang.
My Apacer USB thumb drive is dead, so I can't test out the patch until I order a new one.
The Microsoft Knowledgebase article has been retitled Stop errors occur on a Windows-based computer that has 2GB or more of RAM and is using an NVIDIA nForce USB controller. My computer isn't based on the nVidia chipset, but the update still fixed my hang problem, so I'm not sure why Microsoft retitled the article. I do have 2GB of RAM.