I'm late to the party with Psych. I watched Season 1 a long time ago and since Psych is not available in Canada. I recently rented Season 2 from the library and am now on to Season 3. I wanted to watch them in order for exactly this reason: developing back story lines.
Bringing in Sean's mom is a wonderful addition to the story; I hope that they will keep her around and develop some stories lines around her. It think it could be great fodder for the writers, who do a great job all the time.
I was a bit disappointed in the case's outcome and the premise around it, but the closing scene was wonderful. Imagine after 15 years finding out that one of the foundational beliefs of your life is wrong. Wow.
If anyone is interested in the DVDs, they're well worth renting because they are chock full of extras. Pretty much every episode has deleted scenes and most come with audio commentary.
It's also nice to see a review form my little sis, Teresa. :):)