Conservative talk radio is abuzz with hosts and callers jabbering about reflective requirements for roofing materials. I am a carpenter, not a talker or scientist. What do you say to a gas-bag who is poo-pooing basic energy conservation? Numbers would be good! I can explain that the white-painted section of my roof is much cooler to the touch than the black asphalt section, but I would choke if I had to explain efficiency!
Wet and cold. I repeat, wet and cold. The people in DC are generally good folks, I enjoyed my years there. Be aware of your surroundings and use common sense. It's a fairly safe city as long as you aren't doing anything stupid. Georgetown neighborhood, Dupont and Adam's Morgan are really great places to go out at night. I did just fine on less that $65K. You may have to budget a little bit, but it's worth it. Hit up the obscure monuments while you are there. Everyone goes home with a Lincoln Memorial picture. Get one with the Einstein Memorial. Oh, and the hookers by Chinatown - most of them are dudes.
Here is a link, all it does really is attract the lightning to the rod so it does not hit a building or person.
The weather - cold, fair likelihood of rain/sleet/snow, windy. Did I mention cold? Bring a good coat, gloves, hat, scarf. Safety depends on where you live. There are a few bad areas of town, but overall I feel very safe in the areas I frequent (northwest DC, downtown, Georgetown, Arlington). The people are a mixed bag - they come from all over the country and all over the world. I find people to be friendly overall, but like any big city most people try to stay in their personal space bubbles. There are a lot of young professional people, so you will find a pretty fun social scene.
it is winter time so you have to take all safety regulations. About people there bad and good people everywhere. Good Luck