I also use Address Book for basic contact info.

I use OmniFocus and create projects and tasks for each active contact.

Then I use DevonThink for my contact's notes, attachments, and e-mail archives.

BusyCal is all I really use for a contact solution.

I do miss Now X's ability to show a contact and any attachments and notes in one place. It's a Swiss Army approach (one program to rule them all) but I can see benefits (begrudgingly) in a separate program approach:

1. OmniFocus is better suited at task management than Now X's simple task list. The mythological project/task management module for Now X will never happen.

2. DevonThink is a better place to store my notes than Now X. I can suck in e-mail from Mail.app. I also keep attachments such as spreadsheets, PowerPoint presentations, call history, etc. in here.

3. BusyCal is the program that I wished Now X's calendar would become.

If you are using Contactizer, why not create groups to separate your contacts? Dump the inactives in an inactive group. Then create another group for your most commonly used contacts. Then just work in the commonly used contacts group?

It would be like iTunes. My iTunes master library includes songs from my wife and daughter. But I create a folder in iTunes that holds all my personal playlists. I don't have to weed through my wife's music and my daughter's music. I ignore the master library and just go straight to my own personal library.