I succeeded to hang ubiquity after a lot of attempts. However I can't generate this
behavior by means of the debug-mode.

Procedure :
Boot from live-cd
    WAIT A MINUTE (or more ?)
    From time to time, when pressing Install Ubuntu, the mouse-cursor starts to run,
        but the installer remains on the step first
    In this condition one can close the dialog and quit the installation

File /var/log/installer:

Ubiquity 2.2.8
/usr/lib/ubiquity/ubiquity/frontend/gtk_ui.py:553: GtkWarning: gtk_window_resize: assertion `width > 0' failed
  widget.resize(w, h)
Your console font configuration will be updated the next time your system
boots. If you want to update it now, run 'setupcon' from a virtual console.
update-initramfs is disabled since running on read-only media

Syslog:

ar 26 12:42:41 ubuntu rtkit-daemon[2205]: Watchdog thread running.
Mar 26 12:42:41 ubuntu rtkit-daemon[2205]: Canary thread running.
Mar 26 12:42:42 ubuntu polkitd[2209]: started daemon version 0.96 using authority implementation `local' version `0.96'
Mar 26 12:42:42 ubuntu ubiquity[2179]: log-output -t ubiquity laptop-detect
Mar 26 12:42:45 ubuntu ubiquity[2179]: switched to page language
Mar 26 12:42:49 ubuntu ubiquity[2179]: switched to page language
Mar 26 12:43:35 ubuntu localechooser: info: Language = 'en'
Mar 26 12:43:35 ubuntu localechooser: info: line=en;0;US;UTF-8;en_US.UTF-8;;console-setup
Mar 26 12:43:35 ubuntu localechooser: info: Set debian-installer/language = 'en'
Mar 26 12:43:35 ubuntu localechooser: info: Set debian-installer/locale = 'en_US.UTF-8'
Mar 26 12:43:35 ubuntu localechooser: info: Set debian-installer/fallbacklocale = 'en_US.UTF-8'
Mar 26 12:43:35 ubuntu localechooser: info: Default country = 'US'
Mar 26 12:43:35 ubuntu localechooser: info: Set debian-installer/consoledisplay = 'console-setup'
Mar 26 12:43:35 ubuntu localechooser: info: Set debian-installer/country = 'US'
Mar 26 12:43:35 ubuntu localechooser: info: Set debian-installer/locale = 'en_US.UTF-8'
Mar 26 12:43:35 ubuntu localechooser: info: Selected locale (debian-installer/locale) = 'en_US.UTF-8'
Mar 26 12:43:37 ubuntu ubiquity[2179]: debconffilter_done: ubi-language (current: ubi-language)
Mar 26 12:43:37 ubuntu ubiquity[2179]: Step_before = stepLanguage
Mar 26 12:43:37 ubuntu clock-setup: Fri Mar 26 12:43:37 UTC 2010
Mar 26 12:43:37 ubuntu clock-setup: rdate: adjust local clock by -0.001046 seconds
Mar 26 12:46:15 ubuntu ubiquity[2179]: log-output -t ubiquity setupcon --save-only
Mar 26 12:46:15 ubuntu ubiquity[2179]: log-output -t ubiquity udevadm trigger --subsystem-match=input --action=change
Mar 26 12:46:15 ubuntu ubiquity[2179]: log-output -t ubiquity udevadm settle
Mar 26 12:46:16 ubuntu ubiquity: debconf: DbDriver "targetdb": could not open /target/var/cache/debconf/config.dat
Mar 26 12:46:16 ubuntu ubiquity[2179]: log-output -t ubiquity debconf-copydb configdb targetdb -p ^console-setup/ --config=Name:targetdb --config=Driver:File --config=Filename:/target/var/cache/debconf/config.dat
Mar 26 12:46:16 ubuntu ubiquity: debconf: DbDriver "targetdb": could not open /target/var/cache/debconf/config.dat
Mar 26 12:46:16 ubuntu ubiquity[2179]: log-output -t ubiquity debconf-copydb configdb targetdb -p ^oem-config/ --config=Name:targetdb --config=Driver:File --config=Filename:/target/var/cache/debconf/config.dat
Mar 26 12:46:17 ubuntu gdm-binary[3452]: WARNING: Unable to find users: no seat-id found
Mar 26 12:46:18 ubuntu acpid: client connected from 3458[0:0]
Mar 26 12:46:18 ubuntu acpid: 1 client rule loaded
Mar 26 12:46:18 ubuntu gdm-session-worker[3461]: GLib-GObject-CRITICAL: g_value_get_boolean: assertion `G_VALUE_HOLDS_BOOLEAN (value)' failed
Mar 26 12:46:18 ubuntu pulseaudio[2203]: alsa-util.c: Disabling timer-based scheduling because running inside a VM.
Mar 26 12:46:18 ubuntu pulseaudio[2203]: alsa-util.c: Disabling timer-based scheduling because running inside a VM.
Mar 26 12:46:28 ubuntu acpid: client connected from 3704[109:114]
Mar 26 12:46:28 ubuntu acpid: 1 client rule loaded