Google sent me an invitation to try out Google Wave. I tried it. It didn't work, telling me that it won't run correctly on Internet Explorer, and I should change my browser, preferably to Google's Chrome.
Dear Google! You might want to revisit your mission statement. What you are doing here strongly reminds me of exactly the sort of "evil" anti-competitive practices which got Microsoft into so much trouble with the DoJ and other competition authorities.
My Google Analytics tell me that 25% of my readers use Internet Explorer. Among people on office computers as opposed to private home computers the percentage of users with Internet Explorer is even greater. And on office computers usually you can't just install a different browser, your IT services will have blocked that. So given that Google Wave is probably more useful as a business tool than as a private tool, excluding people with Internet Explorer from using it is an extremely bad idea.
Of course Google will claim it isn't their fault. But if everybody else can get their applications up and running on all different browser systems, I don't think the Department of Justice will buy that excuse. You simply can't develop the "next big thing" in business communication and then use it to beat down a major competitor by making it incompatible with their products. What's next? Google applications that don't run on Windows but only on Chrome OS?