Some really cool things:
- You can use Wave for a sort of instant message-E-mail hybrid, and watch your correspondents typing in real time. (This also means you can see their every typo, which has made me very self-conscious already.)
- It supports embedding videos, images, maps, sudoku games, and a bunch of other things -- even conference calls.
- You can use it to cooperatively edit a document with other people (really useful if you've got a group paper or presentation).
- Playback: If you come in late on a conversation/collaboration, you can press the playback button to see a step-by-step playthrough of all the changes made so far.
- Possibly the coolest thing, at least in my opinion: you can publish directly to a Blogger blog via the Bloggy bot (email@example.com), meaning that you can have collaborative blog posts.
As a note, eBay has numerous listings for Google Wave invitations, ranging from $0.99 for a "nomination" to $199.00 for an active link. Doesn't anyone remember Gmail? It was free -- eventually -- for people who had enough sense to realize it wasn't worth a heap of money to access the beta version a few months early. Still, someone's going to make a nice wad of cash off of the gullible and impatient. And it is a fantastic way for Google to create hype for their product. It's very smart marketing, when you think about it. There's a reason Google will rule the world someday.