I've used DateBK on Treos and it was the main thing that kept me using them. I've been whining for years that I want a grid view in the calendar. That week-at-a-glance view like an old-fashioned paper date book. It's absolutely perfect for my general level of scheduling and really gives me a feel for how my week is shaping up. Unfortunately, I have not heard anything about Pimlico making any BlackBerry version of DateBK. I've tried Pocket Informant for BlackBerry, but I feel it's still not ready.
As for sorting mail into sub-folders, that is a feature of BES. We BIS users just have to do without.