happens here too. Always when I am away, maybe some problem with suspending?

Kubuntu Lucid, all updates installed
Dell Studio 1749 (Intel i520)
Disk: TOSHIBA MK5056GSY

Apr 11 18:57:22 localhost kernel: [ 1852.336426] CPU0 attaching NULL sched-domain.
Apr 11 18:57:22 localhost kernel: [ 1852.336430] CPU1 attaching NULL sched-domain.
Apr 11 18:57:22 localhost kernel: [ 1852.336432] CPU2 attaching NULL sched-domain.
Apr 11 18:57:22 localhost kernel: [ 1852.336434] CPU3 attaching NULL sched-domain.
Apr 11 18:57:22 localhost kernel: [ 1852.415822] ata5: exception Emask 0x10 SAct 0x0 SErr 0x50000 action 0xe frozen
Apr 11 18:57:22 localhost kernel: [ 1852.415827] ata5: irq_stat 0x00400000, PHY RDY changed
Apr 11 18:57:22 localhost kernel: [ 1852.415831] ata5: SError: { PHYRdyChg CommWake }
Apr 11 18:57:22 localhost kernel: [ 1852.415837] ata5: hard resetting link
Apr 11 18:57:22 localhost kernel: [ 1852.429190] CPU0 attaching sched-domain:
Apr 11 18:57:22 localhost kernel: [ 1852.429193]  domain 0: span 0,2 level SIBLING
Apr 11 18:57:22 localhost kernel: [ 1852.429195]   groups: 0 (cpu_power = 589) 2 (cpu_power = 589)
Apr 11 18:57:22 localhost kernel: [ 1852.429199]   domain 1: span 0-3 level MC
Apr 11 18:57:22 localhost kernel: [ 1852.429201]    groups: 0,2 (cpu_power = 1178) 1,3 (cpu_power = 1178)

another one:
Apr 11 14:11:19 localhost kernel: [ 3518.250989] CPU3 attaching sched-domain:
Apr 11 14:11:19 localhost kernel: [ 3518.250990]  domain 0: span 1,3 level SIBLING
Apr 11 14:11:19 localhost kernel: [ 3518.250992]   groups: 3 (cpu_power = 589) 1 (cpu_power = 589)
Apr 11 14:11:19 localhost kernel: [ 3518.250995]   domain 1: span 0-3 level MC
Apr 11 14:11:19 localhost kernel: [ 3518.250997]    groups: 1,3 (cpu_power = 1178) 0,2 (cpu_power = 1178)
Apr 11 14:11:19 localhost kernel: [ 3518.259013] ata5: exception Emask 0x10 SAct 0x0 SErr 0x50000 action 0xe frozen
Apr 11 14:11:19 localhost kernel: [ 3518.259018] ata5: irq_stat 0x00400000, PHY RDY changed
Apr 11 14:11:19 localhost kernel: [ 3518.259022] ata5: SError: { PHYRdyChg CommWake }
Apr 11 14:11:19 localhost kernel: [ 3518.259028] ata5: hard resetting link
Apr 11 14:11:19 localhost kernel: [ 3519.000927] ata5: SATA link up 1.5 Gbps (SStatus 113 SControl 300)
Apr 11 14:11:19 localhost kernel: [ 3519.030125] ata5.00: configured for UDMA/100
Apr 11 14:11:19 localhost kernel: [ 3519.031779] ata5: EH complete
Apr  4 22:53:40 localhost kernel: [    3.288635] ata5: SATA link up 1.5 Gbps (SStatus 113 SControl 300)
Apr  4 22:53:40 localhost kernel: [    3.303600] ata5.00: ATAPI: TSSTcorp DVD+/-RW TS-T633C, D700, max UDMA/100, ATAPI AN
Apr  4 22:53:40 localhost kernel: [    3.303614] ata5.00: applying bridge limits
Apr  4 22:53:40 localhost kernel: [    3.318833] ata5.00: configured for UDMA/100
Apr  4 22:53:40 localhost kernel: [    3.338543] ata5: exception Emask 0x1 SAct 0x0 SErr 0x0 action 0x0 t4
Apr  4 22:53:40 localhost kernel: [    3.338547] ata5: irq_stat 0x40000008
Apr  4 22:53:40 localhost kernel: [    3.340653] scsi 4:0:0:0: CD-ROM            TSSTcorp DVD+-RW TS-T633C D700 PQ: 0 ANSI: 5
Apr  4 22:53:40 localhost kernel: [    3.346733] sr0: scsi3-mmc drive: 24x/24x writer dvd-ram cd/rw xa/form2 cdda tray

and:
Apr  7 21:36:56 localhost kernel: [ 6348.521788] CPU0 attaching NULL sched-domain.
Apr  7 21:36:56 localhost kernel: [ 6348.521794] CPU1 attaching NULL sched-domain.
Apr  7 21:36:56 localhost kernel: [ 6348.521797] CPU2 attaching NULL sched-domain.
Apr  7 21:36:56 localhost kernel: [ 6348.521800] CPU3 attaching NULL sched-domain.
Apr  7 21:36:56 localhost kernel: [ 6348.544835] ata1.00: exception Emask 0x10 SAct 0x0 SErr 0x50000 action 0xe frozen
Apr  7 21:36:56 localhost kernel: [ 6348.544840] ata1.00: irq_stat 0x00400000, PHY RDY changed
Apr  7 21:36:56 localhost kernel: [ 6348.544844] ata1: SError: { PHYRdyChg CommWake }
Apr  7 21:36:56 localhost kernel: [ 6348.544847] ata1.00: failed command: FLUSH CACHE EXT
Apr  7 21:36:56 localhost kernel: [ 6348.544853] ata1.00: cmd ea/00:00:00:00:00/00:00:00:00:00/a0 tag 0
Apr  7 21:36:56 localhost kernel: [ 6348.544855]          res 50/00:80:00:00:00/00:00:00:00:00/40 Emask 0x10 (ATA bus error)
Apr  7 21:36:56 localhost kernel: [ 6348.544858] ata1.00: status: { DRDY }
Apr  7 21:36:56 localhost kernel: [ 6348.544864] ata1: hard resetting link
Apr  7 21:36:56 localhost kernel: [ 6348.600788] ata5: exception Emask 0x10 SAct 0x0 SErr 0x50000 action 0xe frozen
Apr  7 21:36:56 localhost kernel: [ 6348.600792] ata5: irq_stat 0x00400000, PHY RDY changed
Apr  7 21:36:56 localhost kernel: [ 6348.600795] ata5: SError: { PHYRdyChg CommWake }
Apr  7 21:36:56 localhost kernel: [ 6348.600802] ata5: hard resetting link
Apr  7 21:36:56 localhost kernel: [ 6348.604140] CPU0 attaching sched-domain:
Apr  7 21:36:56 localhost kernel: [ 6348.604145]  domain 0: span 0,2 level SIBLING
Apr  7 21:36:56 localhost kernel: [ 6348.604148]   groups: 0 (cpu_power = 589) 2 (cpu_power = 589)
Apr  7 21:36:56 localhost kernel: [ 6348.604154]   domain 1: span 0-3 level MC
Apr  7 21:36:56 localhost kernel: [ 6348.604157]    groups: 0,2 (cpu_power = 1178) 1,3 (cpu_power = 1178)