Following up to myself replying to Greg Troxel's reply to me...

>> So make sure you have umass in your kernel.
[which I did]

> I'm starting to wonder if that card is correctly connected inside
> the machine.

Yup, that was it.  I feel like a prize idiot.  I'm sorry to have
wasted everyone's time, but very thankful for the info that put me on
the right track (card reader probably USB device, should have shown up
as "umass at uhub").  I can't believe I spent hours looking for an
obscure kernel setting when the silly thing was not even connected!

> That's almost certainly what it should look like.

Yes:

umass0 at uhub4 port 7 configuration 1 interface 0
umass0: Generic Mass Storage Device, rev 2.00/1.00, addr 2
umass0: using SCSI over Bulk-Only
scsibus0 at umass0: 2 targets, 4 luns per target
sd0 at scsibus0 target 0 lun 0: <Generic, USB SD Reader, 1.00> disk removable
sd0: drive offline
sd1 at scsibus0 target 0 lun 1: <Generic, USB CF Reader, 1.01> disk removable
sd1: drive offline
sd2 at scsibus0 target 0 lun 2: <Generic, USB SM Reader, 1.02> disk removable
sd2: drive offline
sd3 at scsibus0 target 0 lun 3: <Generic, USB MS Reader, 1.03> disk removable
sd3: drive offline

Hallelujah.  Thanks again!

Anne.