If you've used the iPhone sibling, BeeJive won't be that different to you. You can send files and photos from the app itself, though you can only select from a photo album for the latter. You can record audio messages and share chats with other people through e-mail, customize the wallpaper and toggle sounds among default, Yahoo, AIM or MSN. Emoticons still work, though the ability to use the /me emote is absent. You can also join chatrooms, that feature in and of itself setting BeeJive above its competitors. BeeJive still supports push notification and upon first launch will ask you if you want to enable them -- just make sure not to be alerted for each message if you are in a chatroom!
The main difference is in the interface (see screenshot below). The horizontal view has a three-column view of your buddy list, the current chat window and a list of active chats. The vertical view dispenses with the buddy list column, changing it to a popover you can bring up as needed. The vertical view is preferable for when you're using the iPad's keyboard, as it eats up far too much real estate in horizontal mode.
If you're looking for a solid multi-IM client for the iPad, you won't get much better than BeeJive. It's currently on sale for $5.99 through the App Store, so if you want it, snag it now.
Edit: We have noticed that those using a DiNovo Bluetooth Keyboard are having issues with their text coming out double-spaced. You may want to grab an alternate keyboard or use the built-in one on the iPad until this issue is resolved.