No doubt keeping your Contacts database in check by reducing redundancies is always a challenge, especially with all the multiple syncs we do these days (Exchange, backups, Google, etc.).

One question we get often here at WMExperts is how to remove duplicate contacts on your device, preferably the non-manual way.  Up till now, we recommended the super powerful SKTools (which may be overkill for many).

However XDA member zaijian has created a "still in development" freeware app called Outlook Cleaner and it does the task rather nicely:

How it works
Contact cleaning works like this:
1) Scan the Contacts database, looking for duplicate contacts.
2) Exact duplicates are deleted.
3) Near-duplicates are displayed for manual merging/removal.
4) You go through the sets of near-duplicates, where you can see all the values which are different, and choose to keep, delete, or merge Contacts.

Not too shabby and he promised to add task/calendar cleaning in later versions to make it even more useful.  The app requires .NET CF 2.0, which many of you have already in ROM.  More info including download can be found here.