I own a Zire 71 but am finding there are a couple of options I desperately want on a PDA.
The first is the ability to search the date book for a specific word or event.
The second is a "to do" list that attaches to the date/day and if you don't tick off an item as completed it automatically carries forward
The final option I'm looking for is the ability to do repeating events on no specific pattern (for example, I enter an academic Day 1, Day 2, etc. rotational schedule, but everytime there is a holiday the rotation changes so there is no 'rational' pattern and thus every day needs to be entered individually. I would like to be able to go in and indicate all my day ones by multiple choices on a year's calendar...or some sort of ilk).
The built-in calendar apps on palm and Pocket PC might not have as many features as you'd like. I suggest that you check out the 3rd party calendar programs on both platforms and see if they offer the features you need.