I love this show. I've seen the first 3 seasons. I don't have Showtime though, so it's a bitch to keep up. I should work on getting the DVDs.
I think they have all the seasons uploaded on that website, but I could be wrong. I know they have the current season (Season 5).
Season 4 was a bit boring to me, but Season 5 is picking up really well.
Also, they typically have the new episodes uploaded by the morning after they air. I don't have Showtime, but I've been using that website and it works pretty well.