Well, it is clickable, it doesn’t take to you to twitter search results, but to Google social search results.
But the same tweet viewed in twitter will take you to twitter search result for iPhoneOS4.
Google Buzz already was hyperlinking @userids in tweets to twitter user profiles. As well as Google Buzz has its own @reply mentions to GMail users.
But Google Buzz still does not have hash tags for native buzzes.