If you have multiple devices or switch devices frequently take a look at Google Sync. I use this to keep my contacts, calendar, mail synchronized across 4 mobile devices (on 4 different platforms).
A few things to keep in mind (in order of importance IMO)…
USE COMMON FIELDS – different devices and platforms have different fields for example an iPhone will have an iPhone label but Google contacts, Windows Mobile, Android and Nokia will not. This field therefore will be dropped! Suggested fields are: Mobile, Work, Home, Email
REQUIRES DATA CONNECTION – your PIM data will be stored online under Contacts of your Google Mail so you will need an internet connection at least for 1st run & when you make changes to your databases and you want to reflect these on other devices.
BACKUP – Nothing is 100% full (or fool) proof be sure you have good backups and do regular backups of your devices and your databases. What I do is I export the google.csv every 15th of the month keep a file locally (on my 2nd partition) and keep a file on the cloud (zumo drive) and keep 1 more copy on my USB stick which I leave at home.
This how it looks across my devices.
Windows Mobile Professional 6.1