One of the reasons I think applications like Trumba are important is that I think calendar applications are an area with a lot of potential in the near term.That seems about right. I'd go further though and say that there's been essentially no innovation in any of the core "collaboration" apps. I use the term "collaboration" advisedly because it strikes me as a rather overblown and pretentious use of the word given the sorry state of affairs in software that's supposed to help us work together--especially at remote locations.
a.) There's been essentially zero innovation in them in recent years,
b.) We've all got complicated schedules and
c.) Most of would like some mobile integration (cell phone at a minimum)
What advances we have made have come neither from traditional productivity apps stretching themselves (unsuccessfully for the most part) into a more multi-person context nor form the blaoted, monolithic software that passes for serious collaboration tools. The latter may be useful, or even necessary, in some environments for regulatory and other reasons--but it's hard to see them in the mainstream.
Indeed, the most genuine collaborative innovations have come from the outside. They're lightweight and modular. They're IM and blogs and all the other pieces of software that real people use to communicate and commiserate.