I'll agree with many..
That may be ok in iOS and on my iPad as it is easy to use with touch technology, but as more and more business professionals are adopting mac laptops, iMacs or Mac Pros - that is very unprofessional looking to be on a potential business computer. I know Apple wants to be uniform across devices and we are moving closer and closer to everything being iOS as the main operating system. But seriously, businesses will think that is not professional and we are going back to the non-uniform weird looking DOS-based application days. It is true, there is no uniforminality in the apps in the app store. It is having a consistent UI that made it easier for everyone to adopt Windows back in the day. Every application had the same looking and functionality in the GUI; so there was no learning curve.
That iCal may be easy to use, but is unprofessional looking for potential business computers. Also, many people use ical as it integrates so well with other applications. I still say combine Apple Mail, iCal, and address book into 1 application - so I do not have to have 3 apps open taking up screen space and using more resources. That is what we have in Windows and Linux.
AND KEEP IT PROFESSIONAL LOOKING!
As from what people are posting on the new iCal and Apple Mail, I am afraid the OS is becoming less business intuitive, less functionality, less uniforminality among apps. Something that may hurt Apple more with trying to integrate into the business world.
With the old iCal, I can choose what events I want to see. I can have separate calendars for items, etc. I have several apps that have their own calendar in ical - which allows me turn on or off viewing them with a check box.
edit - Although I am looking forward to a uniformed iChat.