Contact Search in Google Maps will most probably be a future enhancement to Google Maps, especially the mobile version. As of now, it's only a feature in my own imagination.
Here's how the Google Maps Contact Search will work:
When you are on the Google Maps screen, just type 'C'. A search box will pop-up. Start typing in the name of one of your contacts in the box. Google will suggest names from your address book. Select a name and hit enter. Google will show the contact on your map in one or more of the following ways:
1. Display the contact's current location if contact has enabled Google Latitude sharing with you.
2. If you have the addresses for the contact in your address book, those addresses will be shown on the map too.
3. If you are using a phone that has Google Navigation installed on it, you can just tap on one of the contact points on the map and have yourself routed to that spot immediately.