Cyntact is an tweak developed by SaurikIT. LLC, which displays profile pictures in the contact lists.
To display a picture in the contact list, launch Phone.app, choose Contacts and select the contact. Tap Edit, press add photo, either Take Photo or Choose Existing Photo, Move/Scale and then Choose.
Cyntact helps personalize your contacts.
Please note that this has nothing to do with Facebook: this is for viewing the profile pictures you already have stored on your phone. If you would like to synchronize your photographs with Facebook there are App Store applications capable of doing so.
Cyntact is available in Cydia Store for $1.00