Strange. I changed the options to not generate it. Regenerated and tried the simulator and it worked for the Firefox UA. Still not for the two bots I'm checking. (Stummbot and Dnsdigger)

The old sitemap.xml.gz was still there, so I deleted it. Tried again and none of the UAs are working again. Grrr.

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Update: Looks like things were cached. Stumbleupon is working now. (Fingers crossed that it keeps working.) Thanks a ton for the tip. I would never have thought those were related.