Outlook 2010 brings a new feature called suggested contacts, this can be a pain as it syncs to your mobile device (if it uses active sync, iPhone, Nokia, Pocket PC...) and bloats your contact list.

To Turn this feature off select the File Menu

Then Select Options on the Left and then Select Contacts and then remove the tick from Suggested Contacts box at the bottom.

Click OK and your done, no more annoying suggested contacts in your mobile device (you may have to wait for it to sync :)

** Restart Outlook once you have removed  the tick