This is all good advice. I screwed up my hands really bad by ignoring pain and practicing anyway. I couldn't play for about six months. My advice:
1. If it hurts, STOP IMMEDIATELY
2. If you're learning something fast, learn it slow first. When you can play it slowly without pain, your hands will have developed the posture necessary to speed it up in good form. At that point, speed it up slowly. The process usually takes about 5 minutes and you wind up with a much better grasp of the part you're trying to learn to boot. [Side Note: I find this makes the difference, sound-wise, between a kid dorking around in his bedroom and a reasonably serious musical statement.]
3. When you're on the computer, don't keep your hand on the mouse when you're not using it. Try to push your keyboard forward so your arms can lay on your desk.
4. If you think you've done serious damage, take some time away from the guitar. I got thrown so f'ing off course when I screwed up my hands, I would have been a much better player now if I had just sacrificed a week or two to let the damn things heal.
5. Just be more conscious of when your hands/arms start to ache/tingle throughout the course of the day, both on the guitar and off. Being aware of it goes a really long way to keeping your body positioned in such a way that physical stress is minimized.