Instant messaging: iPad loses
On the Mac, Apple's Messages app provides a one-stop shop for instant messaging, supporting AIM, GoogleTalk, Jabber, Yahoo, and Apple's own iMessage service (which works on OS X and iOS only), plus users on local networks. It does text, audio, and video. But the Messages app on the iPad supports just iMessage, making it handy only if your friends and family are all Apple-only users.
The reality is that you'll want third-party apps to handle whatever services you use.