PBS's Young Voices blog discusses shoulder pains and how it could be caused by poor posture when using laptops.  Recommendations include:

1. The top of the viewing screen should be at eye level and arms length away (approx. 20 - 26 inches).

2. Feet should rest flat on the floor (with footrest, if necessary).

3. When sitting upright in the chair, shoulders should be relaxed and comfortable (no slouching) with the lower back against the backrest and the shoulders touching the backrest (a towel or lumbar pad can support the lower back).

4. Thighs should be parallel to the floor and knees at about the same level as the hips.

5. Keyboard height should allow shoulders to relax and arms to rest at sides (a keyboard tray would help).

6. Keyboard should be close (avoid excessive extended reaching).

7. Mouse should be at same level as keyboard.

8. Forearms should be parallel to the floor (about a 90 degree angle at the elbow).

9. And no one should remain in a static position for extended periods of time (even a break every hour would help).