I updated the domU and tried to boot the current linux-image-3.0.0-7-server which unfortunately did not succeed. 
The update and the apport-collect messages were done by booting linux-image-2.6.38-8-server.
When booting 3.0.0-7, the machine hangs with the following output:

[...udev error repeated lots of times...]
udevd[85]: timeout: killing '/sbin/modprobe -bv acpi:PNP0700:' [147]

udevd[85]: timeout: killing '/sbin/modprobe -bv acpi:PNP0700:' [147]

[  723.020104] INFO: task modprobe:147 blocked for more than 120 seconds.
[  723.023759] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[  723.031340] modprobe        D ffffffff81805120     0   147     85 0x00000004
[  723.038795]  ffff88001e1c3ce8 0000000000000086 ffff88001e1c3cd8 ffffffff8139f02c
[  723.047501]  ffff88001e1c3fd8 ffff88001e1c3fd8 ffff88001e1c3fd8 0000000000012a40
[  723.056203]  ffff88001ca08000 ffff88001e2516f0 000000000000632c 7fffffffffffffff
[  723.064872] Call Trace:
[  723.067572]  [<ffffffff8139f02c>] ? vt_console_print+0x2bc/0x3a0
[  723.073365]  [<ffffffff815faca5>] schedule_timeout+0x2a5/0x320
[  723.079017]  [<ffffffff810329a9>] ? default_spin_lock_flags+0x9/0x10
[  723.085111]  [<ffffffff810869b2>] ? up+0x32/0x50
[  723.089672]  [<ffffffff810329a9>] ? default_spin_lock_flags+0x9/0x10
[  723.095784]  [<ffffffff815f9cff>] wait_for_common+0xdf/0x180
[  723.101280]  [<ffffffff81057330>] ? try_to_wake_up+0x200/0x200
[  723.106916]  [<ffffffff815f9e7d>] wait_for_completion+0x1d/0x20
[  723.112634]  [<ffffffff8107c9ad>] flush_work_sync+0x4d/0x60
[  723.118044]  [<ffffffff81078d80>] ? do_work_for_cpu+0x30/0x30
[  723.123635]  [<ffffffffa003bba8>] floppy_init+0x52f/0x5ce [floppy]
[  723.129568]  [<ffffffffa003b000>] ? 0xffffffffa003afff
[  723.134624]  [<ffffffffa003bc47>] ? floppy_init+0x5ce/0x5ce [floppy]
[  723.140754]  [<ffffffffa003bc95>] floppy_module_init+0x4e/0x3b9 [floppy]
[  723.147166]  [<ffffffff81002042>] do_one_initcall+0x42/0x180
[  723.152675]  [<ffffffff8109f3de>] sys_init_module+0xbe/0x230
[  723.158176]  [<ffffffff81604882>] system_call_fastpath+0x16/0x1b
[  723.164015] INFO: task sh:187 blocked for more than 120 seconds.
[  723.169820] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[  723.177396] sh              D ffffffff81805120     0   187      1 0x00000000
[  723.184897]  ffff88001e2e18a8 0000000000000086 0000000000000000 ffff88001f7fcc00
[  723.193594]  ffff88001e2e1fd8 ffff88001e2e1fd8 ffff88001e2e1fd8 0000000000012a40
[  723.202263]  ffff88001ca08000 ffff88001e2e96f0 0000000000000002 7fffffffffffffff
[  723.210953] Call Trace:
[  723.213620]  [<ffffffff815faca5>] schedule_timeout+0x2a5/0x320
[  723.219237]  [<ffffffff8115d040>] ? __mem_cgroup_commit_charge+0x70/0xc0
[  723.225642]  [<ffffffff810329a9>] ? default_spin_lock_flags+0x9/0x10
[  723.231740]  [<ffffffff815f9cff>] wait_for_common+0xdf/0x180
[  723.237218]  [<ffffffff81057330>] ? try_to_wake_up+0x200/0x200
[  723.242867]  [<ffffffff815f9e7d>] wait_for_completion+0x1d/0x20
[  723.248592]  [<ffffffff8107ca4e>] flush_work+0x2e/0x40
[  723.253636]  [<ffffffff81078d80>] ? do_work_for_cpu+0x30/0x30
[  723.259184]  [<ffffffff81392f95>] tty_flush_to_ldisc+0x15/0x20
[  723.264841]  [<ffffffff8138d254>] n_tty_poll+0x64/0x1e0
[  723.269940]  [<ffffffff81389dc2>] tty_poll+0x92/0xa0
[  723.274839]  [<ffffffff81178792>] do_poll.isra.4+0x102/0x290
[  723.280337]  [<ffffffff81179799>] do_sys_poll+0x1b9/0x240
[  723.285625]  [<ffffffff81178410>] ? poll_freewait+0xe0/0xe0
[  723.291037]  [<ffffffff813918cb>] ? put_ldisc+0x5b/0xc0
[  723.296137]  [<ffffffff8139193e>] ? tty_ldisc_deref+0xe/0x10
[  723.301618]  [<ffffffff8139068e>] ? tty_set_termios+0x10e/0x270
[  723.307326]  [<ffffffff812e1d4e>] ? radix_tree_lookup_slot+0xe/0x10
[  723.313360]  [<ffffffff811081ee>] ? find_get_page+0x1e/0x90
[  723.318764]  [<ffffffff81109f47>] ? filemap_fault+0x87/0x3c0
[  723.324279]  [<ffffffff8110788a>] ? unlock_page+0x2a/0x40
[  723.329528]  [<ffffffff8112a219>] ? __do_fault+0x439/0x510
[  723.334880]  [<ffffffff8112d50a>] ? handle_pte_fault+0xfa/0x210
[  723.340598]  [<ffffffff8112d9d8>] ? handle_mm_fault+0x1f8/0x350
[  723.346372]  [<ffffffff81600050>] ? do_page_fault+0x210/0x530
[  723.351950]  [<ffffffff8138d8a0>] ? process_echoes+0x30/0x30
[  723.357436]  [<ffffffff81165e00>] ? vfs_write+0x110/0x180
[  723.362690]  [<ffffffff81179906>] sys_poll+0x76/0x110
[  723.367659]  [<ffffffff81604882>] system_call_fastpath+0x16/0x1b
udevd[85]: timeout: killing '/sbin/modprobe -bv acpi:PNP0700:' [147]

udevd[85]: timeout: killing '/sbin/modprobe -bv acpi:PNP0700:' [147]

[...udev error repeated lots of times...]

udevd[85]: timeout: killing '/sbin/modprobe -bv acpi:PNP0700:' [147]

[ 1994.980069] INFO: rcu_sched_state detected stall on CPU 0 (t=269277 jiffies)
[ 4894.160143] INFO: rcu_sched_state detected stall on CPU 0 (t=489180 jiffies)
[ 4894.163328] INFO: rcu_sched_state detected stalls on CPUs/tasks: { 0} (detected by 1, t=489180 jiffies)
udevd[85]: timeout: killing '/sbin/modprobe -bv acpi:PNP0700:' [147]

udevd[85]: timeout: killing '/sbin/modprobe -bv acpi:PNP0700:' [147]

[...udev error repeated lots of times...]