I get on Twitter sometimes and see what people are saying about Unicode or other topics of interest. You can participate via the web or use one the large number of dedicated apps.
Twitter supports Unicode, but some apps are better than others. With Tweetdeck, you need to set the font preferences to International. Neither Tweetdeck nor Seesmic will display complex scripts like Hindi correctly, but Tweetie and Echofon do. Those are the only ones I've tried so far.
Jim DeLaHunt has done a survey of language use on Twitter, check out this page. The top 5 are English, Portuguese, Japanese, Spanish, and German.