Skype is without a doubt the most broken piece of communications software that you will find anywhere. It built its reputation on its video and audio call functionality, but both are embarrassingly badly implemented. I don't even know whether the echo-cancelling algorithm can be called such, because every call is an irritating mess of noise and audio feedback. It has a latency of about half a second, which is enough to make every participant of a conversation constantly puzzled about what the other participant(s) might have been saying. Microsoft has done echo cancellation better in their Messenger and NetMeeting/Lync tools for over 10 years, so I don't understand why Skype can't get it right. On top of that, video quality is awful and unreliable, which becomes clear once you directly compare them to alternatives such as Google Hangouts or, again, Windows Messenger.
Alright, so you fall back to the text IM functionality, and this is where the fun really starts! Because the protocol is so unreliable that several of my friends have resorted to actually calling their conversation partners after a while, in order to ask them whether they received their Skype IM messages. Surely, this can't be the purpose of an IM solution. Since Skype refuse to extend their P2P model with server-client functionality where it would be helpful, there will probably also never be a working offline messaging functionality. Which means that unless your contact is online at the same time as you, you'll have to revert to mobile text messages to contact them. Also for the same basic reasons, the conversation history synchronisation is utterly broken, delivering old messages to you as new ones again, up to as many times as the number of devices/systems you use Skype on. There's nothing as irritating as being delivered "new" messages when one of your contacts signs in, replying to them, then noticing that you've just replied to messages that were two weeks old, because Skype is too stupid to remember which messages you've already seen.
In summary, none of the three basic channels offered by Skype really work, making the entire network and solution absolutely useless for communication. Unless you are forced to use this because of co-workers etc. (in which case you will have to use it, because Skype is the only IM solution that, thanks to Skype's policies, isn't integrated into any of the multi-protocol IM clients), steer way, way clear of this turd.