I, like so many others, am absolutely obsessed with this show. It's a Masterpiece Classic miniseries that I watch on pbs.com, which is fabulous because it has no commercials. It's written by the same writer who did Gosford Park, and you can really feel the similarities as you watch the show - the same intrigue and hint of scandal that wafts through the upper and lower floors of this massive estate amongst the household and its staff. The main difference (and downside) is that there's no Clive Owen in Downton!
If you haven't gotten into this show, I highly recommend it. I watched the entire first season in one weekend months ago, and I'm watching the second season now. It's over in the UK but it's still coming out here in the US.