Hi
I have planned to stay in NY 4 days then 4 days in Boston and 3 days in Washington - is 4 days sufficient for NY- I hope to visit all the well known places - any suggestions - same for Boston and Washington DC. Thank you
NEW YORK
4 days in NYC is probably enough if you make a good plan of what you want to do. You could definitely split all the time between just two cities if you wanted, though I understand wanting to visit more places.
You sure can if you don't expect to see everything. A good idea is take the bus tour (go with Greyline, they're a few dollars more but worth it) downtown and uptown early then wander around using the subway once you know approximately where everything is.
My girlfriend and I just spent 10 days there over Christmas. We got to know the city really well.
The lineup(s!!) for the Statue of Liberty is 3hr (one line for tickets, one for the boarding). So that's a whole day thing.
Prepare to be checked for security again and again and again at almost every attraction.
Visit the Hans Christen Anderson statue in Central Park east (near the Alice in Wonderland statue towards the south west). Everyone likes the Alice statue. He seems so lonely. Poor guy.....
I did NYC in 5 days, but 4 would be fine if you know where you want to go.
One tip - the Staten Island Ferry is free and will take you out for a fantastic photo op of the Manhattan skyline and Lady Liberty. At the other end we just walked straight through the terminal and back onto the returning ferry. The whole trip took about an hour and gave us some fantastic pictures.
Sarah
P.S in Washington DC I think 3 days is great. If you want to see all the famous sites on the cross-layout (White House, Capital Hill, memorial etc) they can be done in one-long walking day. This is how I saw it and it was excellent.
Have a great time
For New York I did 6 days and I even had the time to check some other (off the program places on my own...) My suggestion is check what you want to see first, check in the map, there are thousands of maps for free everywhere, starting from your hotel desk, and I did a lot of walking so have good rest for the days are long and non stopping, but 4 days? I think it is just fine as long as you try to make the best out of these.
Getting a transport 15 day pass is worth buying for the endless subways and busses you will be taking do your numbers and you will realize it is cheaper.
As for the Statue of Liberty, do it same day you will do the Staten Island ferry you will have pics from far and close then, try going there early really early so you avoid the crowds! same at the empire state...
Divide the city in areas so you go one by one and then if time allows repeat some of these.
By the lunch time you will have done lots of things and that allows time even for shopping!! yess! 
HAVE A GREAT TIME!!
I did most things in New York in a week but if you plan it I think you can get everything done in 4. It might be a push though!
Interesting this topic should come up, I went last August and have wrote a diary about my trip:
-snip-
Have a great time 
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avoid the subway! it's confusing plus if you stay above ground, you see more!
I loved Boston, thought it was a fantastic place and cant wait to go back later this year.
There's the obvious tourist attraction of the Cheers barS (One is the Bull and Finch which is where the exterior shots were taken and One is a replica bar in Faneil (Spelling) Market).
The freedom trail is a fab walk, you follow the red bricks around the whole trail seeing the likes of Paul Revres house and old ironsides (War ship) and many other fab things.
Also take the time to take a "Duckboat" tour, they are fantastic fun. Basically old world war ampibious crafts that drive around the city and into the river.
I cant talk highly enough about Boston.
I disagree about totally avoiding the subway. Taking it can be an adventure in itself. Some of the stations have beautiful artwork and there are often performances which are great to watch, especially in the bigger ones.