Here's my picture-postcard view of the White House (south side), taken on Sunday morning:
About 5 hours later, we walked back by, and there was more security. We had to stay across the road from the fence this time.
My story is that I saw the Obamas walking towards the trees on the left, and heard kids calling out from the grounds. (Really, I was too far away to tell who the couple was, and I wasn't positive the call I heard came from the White House grounds. But I like my story, and the enhanced security backs it up).
On the north side, there was a mounted patrolman. He was alert, but his horse looked fairly relaxed.