Comment 3 for bug 750592

Something similar is happening to me as well - 3 different SDHC cards (kingston and sandisk) on an Acer Aspire 5742. I can mount them fine if I use an external USB card reader.

The disk utility shows them, but they attempt to mount to /

This is all that shows up in dmesg on card insertion:
 00:00:00:00:00:00
[ 361.991210] sd 4:0:0:0: [sdc] 31457280 512-byte logical blocks: (16.1 GB/15.0 GiB)
[ 361.993322] sd 4:0:0:0: [sdc] No Caching mode page present
[ 361.993329] sd 4:0:0:0: [sdc] Assuming drive cache: write through
[ 361.996583] sd 4:0:0:0: [sdc] No Caching mode page present
[ 361.996590] sd 4:0:0:0: [sdc] Assuming drive cache: write through
[ 361.997438] sdc: sdc1

When I first upgraded to 11.04 beta (from alpha), the card reader worked. It also worked on 10.10.