We had exactly the same problem recently. vis: 

machine/config::
-----------------------
SamSung Series 3 Laptop - NP350E7C-S02UK - Intel core ii7 quad 3.6GHz, 64 bit, RAM: 8GB, HDD: 1TB - Windows 8 partition at start, Ubuntu partition at 500GB mark - dual bootable via BIOS only (due to ntfs boot partition distance limit).

Ubuntu: 12.04.2 LTS
 
Skype: 4.1.0.20 - installed via Dash Home, Applications menu, run from icon in Ubuntu applications sidebar
Skype Options: (as set up by default)::
 - Video Devices: webcam = SC-13HDL11939N(/dev/video0) - {only option}; Disable Auto Exposure = UNchecked
 - Sound Devices: device='default' (for Microphone and Speakers and Ringing); automatically adjust mixer levels = checked
 -- *** NOTE: around a dozen other sound devices (mostly Intel) are also shown as available, including one named just 'Pulse' - this is UNEXPECTED!

 -- NOTE: also - no skype icon appearing in Ubuntu top dash/menu area - this is unexpected  
 
Symptoms:
----------------
 - skype self test - sound effects and test call - appeared to work fine
 - during voice only or voice+video calls (skype to skype), incoming or outgoing - skype would suddenly close/crash at RANDOM times between a few minutes and 20 mins into call (otherwise call quality good)
 - during voice only or voice+video calls (skype to skype), incoming or outgoing - skype would suddenly close/crash REPRODUECABLY whenever attempting to either send or receive skype text message to same user within call

 - upon crash, skype would still leave an active process running and would still convey skype notification 'bubles'/sounds
 - skype could be relaunched ok by clicking Ubuntu applications sidebar icon in normal way, ie. without killing process - but resulting in same crash symptoms eventually
 
Remedies attempted:
-------------------------------
 - killing old skype process, before attempting skype relaunch - same symptoms
 - skype options, video devices: 'Disable Auto Exposure'=CHECKED - same symptoms
 - skype options, audio devices: 'automatically adjust mixer levels'=UNCHECKED - same symptoms  
 - skype options, audio devices: device='Pulse' (for Microphone and Speakers and Ringing) - same symptoms + NO voice sound audible from caller (though ringing and outgoing sound (audible by caller) ok).
 
Remedies that worked::
----------------------------------
The following procedure fixed the problem: for us:

 - close and quit skype.

 - then from terminal session::
 - remove and purge existing skype install::

$ sudo apt-get autoremove --purge skype
 - ok

 - make sure system up to date::
 
$ sudo apt-get update && sudo apt-get upgrade 
 - nothing to do - ok

(NOTE: we still got incoming skype notifications bubbles popping up at this stage - HOW!!!? (maybe i should have killed any existing skype process also))

 - reboot machine (to be on safe side), then, from terminal session again::

 - ensure we are looking at canonical partner apps repository:
 
$ sudo add-apt-repository "deb http://archive.canonical.com/ $(lsb_release -sc) partner"
 - ok

 - check all updated again for good measure and install skype from there::
 
$ sudo apt-get update && sudo apt-get install skype
 - ok 
 
 - run/test skype again from Ubuntu dash Home, Apps - note: do not run recently run version, but choose again from main 'Installed Apps' section - to be on the safe side

After procudure above::
-------------------------------------
 - skype launches  - OK
 - skype options show following::
 -- Skype Version: 4.1.0.20 - this is showing same version as before!
 -- Sound Devices: device='PulseAudio server (local)' for Microphone and Speakers and Sound! 
 --- *** NOTE: this is now the ONLY device available (no strange Intel drivers or just 'Pulse' available anymore)! 
 -- Video Devices: still set as before
 -- 'Disable Auto Exposure' and 'automatically adjust mixer levels' - are unchanged from before 
 
(NOTE: skype logged into account automatically, without asking for password, as previously set before - ie. reinstall purge did not appear to have removed skype profile/config settings from home dir. no problem).


Testing:
-----------
 - skype self tests, sound and call - ok
 - so far, no crashes during either incomming or outgoing calls - sound or sound+video - call quality good - ok
 - NO crashes whilst sending or receiving skype text messages during calls
 - file transferes during calls - ok 
 - Skype Icon NOW apears Ok in Ubuntu top dashboard menu - ok
 
IE: everything appeares to be working fine!


Sugested causes of original problem:
------------------------------------------------------
 - possibly installing skype through Ubuntu dashboard Home, Install Apps menu, uses different driver/install configuration to that used by terminal setup above using Canonical partner repos, else possibly entirely different skype app itself. 
 - possibly also, some previous applications install (eg; 'Mixx' application) had overwritten some drivers.
 
 - It would be great if someone wit better knowledege could take a closer look at the internals here to verify.

Hope this helps someone else.