Wort reports that the Saudi authorities have threatened to block access to Skype, WhatsApp and Vibre. Officially this is due to the harm caused by such services which often circumvent national telcos to provide free or effectively zero charge (beyond data costs) messaging, chat and video. Unofficially this is almost certainly down to censorship reasons, many countries such as UAE block Skype (or atleast try to) on account of the systems using encryption to prevent the state snooping on calls. Iran does however tolerate Oovoo (the Skype alternative) which does not encrypt data. It is worth noting though that Skype now stores it’s encryption keys centrally therefore making it much easier for nice authorities such as those in the UK and USA to monitor your calls. Interestingly Wort also reports that Blackberry (previously RIM) managed to get it’s messenger service past UAEs censors, quite exactly how remains interesting. The British authorities had serious issues with RIM (Blackberry) during the riots a few years ago due to the encrypted messages being used to organise rioters. India also threatened to cut off Blackberry for the same reason. In both cases though Blackberry were allowed to continue… exactly why is not clear.
Wikipedia has a nice article on Skype security (and privacy). Among the interesting points are that a Skype representative refused to say if they do eavesdrop and that Russian authorities can intercept Skype calls without any court process. Skype for Linux also scans the /etc/password file which it has no legitimate reason.
As a side note if you are using services with US based servers then all non-US nationals data is automatically scanned anyway. In any event I will continue to use as the authorities will surely find my discussions with family and friends beyond normal levels of excitement.