While I don't think that I'm going to use it – my calendaring needs are extremely minimal – I think that this is a really interesting application from a user interaction perspective, and would encourage you to check it out.
What really makes Caliander stand out as an application is what it calls a "Perceptual Log" view. The screen is broken into vertical bars representing a period of time. Depending on which view you're in (day, week, month) the bars will be as small as an hour or large as a day. When you click and drag one of the bars, the bars on either side will shrink or expand and you will see more of the future or the past depending on which way you are dragging.
Since my calendaring needs are almost non-existent I don't think I'll end up using this, but I may try creating a widget to do logarithmic timelines on the web if I have some free time. This is very interesting and I hope the author is successful in the Mac App Store!
You can check out Caliander here