On my Titanium Powerbook 500:
(Linux dearborn 2.4.13-ben0 #1 Fri Oct 26 21:48:08 CDT 2001 ppc unknown)

ieee1394: NodeMgr: hotplug policy returned 0xfffffffe
ieee1394: Device added: node 0:1023, GUID 0000000002002f0d
ieee1394: sbp2: Driver forced to serialize I/O (serialize_io = 1)
ieee1394: sbp2: Node 0:1023: Max speed [S400] - Max payload [0x09/2048]
scsi1 : IEEE-1394 SBP-2 protocol driver
  Vendor:           Model:                   Rev:     
  Type:   Direct-Access                      ANSI SCSI revision: 03
Attached scsi disk sda at scsi1, channel 0, id 0, lun 0
SCSI device sda: 9780750 512-byte hdwr sectors (5008 MB)
 /dev/scsi/host1/bus0/target0/lun0: [mac] p1 p2 p3

[root@dearborn /var/log]# mac-fdisk -l /dev/sda
/dev/sda
        #                    type name                length   base    ( size )  system
dump: name /dev/sda len 8 
/dev/sda1     Apple_partition_map partition map            3 @ 1       (  1.5k)  Partition map
/dev/sda2              Apple_MDFW firmware             65536 @ 4       ( 32.0M)  Unknown
/dev/sda3               Apple_HFS disk               9715210 @ 65540   (  4.6G)  HFS

Block size=512, Number of Blocks=9780750
DeviceType=0x0, DeviceId=0x0


[root@dearborn /var/log]# hpmount /dev/sda3
[root@dearborn /var/log]# hpls -a
                         .VolumeIcon.icns         iPod_Control
.                        Desktop DB               TheVolumeSettingsFolder
.DS_Store                Desktop DF
.Trashes                 Icon?
[root@dearborn /var/log]# hpcd iPod_Control      
[root@dearborn /var/log]# hpcd Music
[root@dearborn /var/log]# hpls -a
.    F01  F03  F05  F07  F09  F11  F13  F15  F17  F19
F00  F02  F04  F06  F08  F10  F12  F14  F16  F18
[root@dearborn /var/log]# hpls -a F11
.                                FYR.mp3
12_Der_Schl_ssel.mp3             Herbs_ Good Hygiene _ Socks.mp3
69_Love_Songs_1_02_I_Dont_B.mp3  Home.mp3
69_Love_Songs_2_05_Very_Fun.mp3  Kool_Keith___Office_Space_S.mp3
69_Love_Songs_2_11_My_Only_.mp3  Low Kick and Hard Bop.mp3
69_Love_Songs_2_14_Washingt.mp3  Matter vs. Space.mp3
69_Love_Songs_2_17_Papa_Was.mp3  Method Man and Redman _ D 1.mp3
69_Love_Songs_3_17_Two_Kind.mp3  Method Man And Redman _ Da.mp3
8_My_Wandering_Days_Are_Ove.mp3  Run Run Run.mp3
Aaliyah_feat_Timbaland_Are_.mp3  Solex In A Slipshod Style.mp3
Absentee.mp3                     The Dot on the i Between th.mp3
Closer.mp3                       The News _A Wholly Owned Su.mp3
Five Star Shamberg.mp3           Waking Up With Solex.mp3
[root@dearborn /var/log]# hpcd F11
[root@dearborn ~]# cd /tmp/
[root@dearborn /tmp]# hpcopy Closer.mp3 .
[root@dearborn /tmp]# file Closer.mp3 
Closer.mp3: mp3 file with ID3 2.0 tag

So, mp3 files can be copied off the iPod.