I vacationed there for the same thing pre-9/11, so can't speak for current security restrictions, but have some general tips:

Plan on using the Metro to get around in the city. It's actually quite efficient (or was when I visited), and driving and parking in the city are both nightmares.

When crossing an intersection, watch out for drivers shooting the yellow and for ones jumping the green. I'm amazed I never saw a collision in the week I was there.

I was there in the Spring, too, and the weather can change completely from one day to the next. Take both sun and rain protection.

Expect lines. Carry water.


And have fun!