What happens if you boot with the SD card in place?
This seems very curious.  I think you're close, though.  I've successfully
read CF and MMC cards with my multimedia reading device.  I thought MMC
cards were similar to SD cards, and, in fact, my device shows up as an
MMC/SD reader.
	There was a patch back in September from Nathan W to the USB system
which addressed the bulk stalled messages, but I'm not sure which branches
it was applied to.  I thought it was applied to2.1, 2.0  and 3.0. I know
it's applied to 3.0, but I'm not sure about 2.1. cvsweb.netbsd.org should
tell you, though.  It's an easy patch to apply, if you don't have it, and
it makes a world of difference respecting the way USB devices work under
NetBSD.  
Hope that helps.
-Brian