As others have said, there can be big losses on the scale your first week or two, especially if you have a lot to lose. A lot of it is excess fluid weight, although certainly some fat too. It's always nice to be a little closer to the ultimate goal than you thought!
Don't be disappointed when things slow down a bit, and you start seeing the usual 1-2 pounds a week. That's more typical -- and though it feels slow while you're doing it, those 1-2 pound losses will add up fast!
Starting Weight: 260 lbs. (November 2010)
Quasi-Maintenance: 165 lbs. (June 2011)
Goal Weight: 150 lbs. (reached December 8, 2011)
Size 22W to Size 4
Currently maintaining within 5 lbs. (+ or -) of goal. I weigh daily, but also use a tape measure and the fit of my clothes to guage how well I'm doing.