I think I have seen the same problem.  I am running an up to date breezy badger and whenever I write to my 256 MB Sweex usb pen drive the write hangs.  I've used this same pen drive on a number of linux-2.4 based machines with no problem.

I wanted to eliminate gnome,  so I disabled automount in "Preferences", inserted the pen drive,  mounted /dev/sda from the command line, and tried to copy around 40MB of files.  It still took about 10 times longer than I would expect to finish copying, and the "umount" hung forever!

By this point I was sure it was the kernel usb system to blame.  In order to eliminate the filesystem I tried just copying data directly:

       dd if=dosfs.img of=/dev/sda # where dosfs.img is a 22 MB file

This also hung forever.  I looked at /var/log/messages and found that it was generating masses of lines of output, so I just removed the usb pen drive and they stopped.  Here are the first few lines:

Feb  9 08:36:11 localhost -- MARK --
Feb  9 08:53:19 localhost kernel: [4511832.187000] usb 1-1: new full speed USB device using uhci_hcd and address 35
Feb  9 08:53:19 localhost kernel: [4511832.323000] scsi13 : SCSI emulation for USB Mass Storage devices
Feb  9 08:53:20 localhost usb.agent[26127]:      usb-storage: already loaded
Feb  9 08:53:24 localhost kernel: [4511837.329000]   Vendor: ICSI      Model: MP3 PLAYER FLASH  Rev: 1.0A
Feb  9 08:53:24 localhost kernel: [4511837.329000]   Type:   Direct-Access                      ANSI SCSI revision: 00
Feb  9 08:53:24 localhost kernel: [4511837.341000] SCSI device sda: 512000 512-byte hdwr sectors (262 MB)
Feb  9 08:53:24 localhost kernel: [4511837.347000] sda: Write Protect is off
Feb  9 08:53:24 localhost kernel: [4511837.363000] SCSI device sda: 512000 512-byte hdwr sectors (262 MB)
Feb  9 08:53:24 localhost kernel: [4511837.369000] sda: Write Protect is off
Feb  9 08:53:24 localhost kernel: [4511837.369000]  /dev/scsi/host13/bus0/target0/lun0:
Feb  9 08:53:24 localhost kernel: [4511837.441000] Attached scsi removable disk sda at scsi13, channel 0, id 0, lun 0
Feb  9 08:53:24 localhost scsi.agent[26173]:      sd_mod: loaded sucessfully (for disk)
Feb  9 08:55:30 localhost kernel: [4511963.259000] SCSI error : <13 0 0 0> return code = 0x10070000
Feb  9 08:55:30 localhost kernel: [4511963.259000] end_request: I/O error, dev sda, sector 0
Feb  9 08:55:30 localhost kernel: [4511963.259000] printk: 3132 messages suppressed.
Feb  9 08:55:30 localhost kernel: [4511963.259000] lost page write due to I/O error on sda
Feb  9 08:55:30 localhost kernel: [4511963.387000] SCSI error : <13 0 0 0> return code = 0x10070000
Feb  9 08:55:30 localhost kernel: [4511963.387000] end_request: I/O error, dev sda, sector 8
Feb  9 08:55:30 localhost kernel: [4511963.387000] lost page write due to I/O error on sda
Feb  9 08:55:30 localhost kernel: [4511963.526000] SCSI error : <13 0 0 0> return code = 0x10070000
Feb  9 08:55:30 localhost kernel: [4511963.526000] end_request: I/O error, dev sda, sector 16
Feb  9 08:55:30 localhost kernel: [4511963.526000] lost page write due to I/O error on sda
Feb  9 08:55:30 localhost kernel: [4511963.663000] SCSI error : <13 0 0 0> return code = 0x10070000
Feb  9 08:55:30 localhost kernel: [4511963.663000] end_request: I/O error, dev sda, sector 24
Feb  9 08:55:30 localhost kernel: [4511963.663000] lost page write due to I/O error on sda
Feb  9 08:55:30 localhost kernel: [4511963.822000] SCSI error : <13 0 0 0> return code = 0x10070000
Feb  9 08:55:30 localhost kernel: [4511963.822000] end_request: I/O error, dev sda, sector 32
Feb  9 08:55:30 localhost kernel: [4511963.822000] lost page write due to I/O error on sda
Feb  9 08:55:30 localhost kernel: [4511963.949000] SCSI error : <13 0 0 0> return code = 0x10070000
Feb  9 08:55:30 localhost kernel: [4511963.949000] end_request: I/O error, dev sda, sector 40
Feb  9 08:55:30 localhost kernel: [4511963.949000] lost page write due to I/O error on sda
Feb  9 08:55:30 localhost kernel: [4511964.066000] SCSI error : <13 0 0 0> return code = 0x10070000
Feb  9 08:55:30 localhost kernel: [4511964.066000] end_request: I/O error, dev sda, sector 48
Feb  9 08:55:30 localhost kernel: [4511964.066000] lost page write due to I/O error on sda
Feb  9 08:55:31 localhost kernel: [4511964.181000] SCSI error : <13 0 0 0> return code = 0x10070000
Feb  9 08:55:31 localhost kernel: [4511964.181000] end_request: I/O error, dev sda, sector 56

Hope this is helpful, and BTW, I'm still really impressed with ubuntu!