Thanks, guys. Honestly, I feel much like I did after getting my Bachelor's - a little underwhelmed. I think that's partly because it doesn't change what I do much; since I'm pursuing a Ph.D., this is a milestone and not an end in itself. The other part is the reaction I got from my advisor on the presentation itself.
To answer Sine's question, yes, I had to defend my work. I gave an hour long presentation, and then answered questions. I had a committee which consisted of my advisor and two other professors. The other members of my committee seemed satisfied with my work, my presentation of it, and my answers to their questions. But my advisor himself didn't seem pleased with my presentation, which is rather typical of him.