I've been a NUDC and NowX user for about 15 years, and much of my professional life is recorded in my calendar and contacts. (Including detailed notes attached to individuals, companies and appointments.) Moving to something as simple as the iCal and Address Book apps won't really cut it for me. The primary feature I've relied on NUDC for is the ability to link a contact to a given appointment or other kind of calendar "event", and that opening the contact will show me all that history too.

NowX was looking promising, despite its quirky bugs. The one feature in NowX that has not been working for me (and really it's because of synching I believe) is tasks, particularly recurring tasks. It's been a nightmare. I'm not sure whether I should blame Now, Apple's email client (where the to-do list lives, which is strange to me) or perhaps MarkSpace's Missing Sync or Palm.

Tasks aside, is there a calendar and contact management app that has a system for multiple categories and independent tags that allows individuals or companies in the contacts list to be linked to appointments?

I haven't seen one but would love to find a replacement.