Flashes Before Your Eyes/Theories - Lostpedia:
#Penelope knows that to find Desmond she needs to detect a large electromagnetic anomaly because Desmond told Donovan all about The Island and The Swan. Donovan and Penelope must have spoken, probably sometime after Desmond left on the race (or within 3 years of that time), so she set up the Listening Station.
# The reason we did not see Penelope until the second season finale is because she was not looking for Desmond until after the hatch exploded. In the original timeline, prior to Flashes Before Your Eyes, Desmond was lost and Penny moved on (or something to that effect). In the new timeline, Penny is able to look for Desmond based on the above note. So, prior to that episode, nobody was looking for the Oceanic survivors, but thanks to Desmond, that changed. This fact was so difficult for the average viewer to see because not only did the hatch explosion change the past, it is also the event that the Listening Station used to find the island. The hatch explosion basically served two huge purposes towards getting everyone rescued.
no theory involving the ring. I wonder if we will see it again.
no reason it needs to reappear significantly - just the way the camera followed it when Desmond threw it into the water - makes me want it to figure later..