The appropriateness of tegus as pets varies with the species. Columbian tegus and gold tegus tend to be very skittish. While some can be handled, they generally try very hard to avoid it. Red tegus are friendlier than the columbian and gold, but they are still somewhat shy.
Argentine black and white tegus make excellent pets. They are very intelligent and extremely friendly. They are interested in people, including new people, and like to know what is going on. They can learn their name and be trained to come when called. When adult sized, they will sleep in your bed with you if you wish. T. merianae is omnivorous and very easy to feed -- while their diet should be balanced and moderately rodential, you can feed them nearly any table scraps. They like fruit such as strawberries, oranges, and cantaloupe. They are especially cute when eating left-over chinese takeout.
Information is culled from personal experience with T. merianae and from Agama International