The -D switch tells it to download, the -R coupled with -s and -t switches tell it to re-download between a certain date range... well, at least it's supposed to, but it doesn't work.
UMDS needs a major overhaul to:
1. Let me choose which versions to download patches for. I don't have, never have had, and never will have ESX 3.0, so why should I download those patches. There should be a config file setting to set the versions you want something akin to: Vesions=35,40
2. Rather than downloading everything or specifying a date range to re-download:
Download a listing of available patches for the versions I have specified
Compare that listing to what is in my local repository
Download only the differences
3. Provide a way to cleanup a repository to remove patches that are no longer needed.
It cannot be good for VMware to have everyone repeatedly downloading multiple gigabytes of patches from them all the time.