The previous answers to this question are misleading. You can only watch recorded shows if they are available as an 'on demand' show. You can not watch any DVR recorded shows due to, according to AT&T, a 'licensing issue'.
Yes, you can watch your AT&T recorded DVR shows online. You can use U-verse Online to plan DVR recordings straight from the web. If you're not at home and would like to see which of your recordings you can watch on U-verse Online, you can choose "My U-verse DVR" to see exact episodes and movies to watch right away with U-verse Online.