When you say, "lets Skype", you usually want to have a video call. That is what made Skype popular, and where its strength lies. However, lately Microsoft has also been focusing on written conversation, perhaps in reaction to how successful IM apps have been.
Microsoft updated Skype last week to 7.0 on Mac and Windows (beta), and one of the features overlooked in the UI redesign was formatting for instant messaging. You can now bold, italicize, or strike-through your messages.
The commands are very simple, you can bold with *asterisks*, italicize with _underscores_ and strike-through with ~tildes~.
It is usually hard to express your emotions clearly through text, but with animated emoji and now formatting, Skype lends your words more voice than other IM solutions. It will be interesting to watch if Microsoft takes the text formatting further, although that could make chats unnecessarily messy.
There are still problems with the instant messaging experience of Skype. The biggest one is annoying, space-consuming ads on the desktop, especially since (practically) no other messaging app subjects their users to any. The ads don't affect the video messaging experience, but Microsoft will have to fix up some things if it wants to compete with the likes of Facebook messenger, Google Hangouts, or Apple's iMessage.