The problem with weed is that most of the time smoking it makes you mellow.....not exactly condusive to starting a revolution!
However, I think it's fully possible to indulge in it AND be a responsible citizen and it's a shame that the younger generation doesn't make more of an effort to vote and get more liberal people into office.
I do think a big march in Washington could be very effective if the people marching conducted themselves in a respectful and intelligent way. We aren't going to win any battles by representing the sterotype of a bunch of lazy and dumb stoners. Instead, it would be great to send a message that you can smoke and still have productive lives. And the point should be made that it's much less harmful than other legal substances.
No, a march like this isn't going to change laws overnight, but what's even more important is that if it was done *right* it would get good media coverage and would perhaps educate people and make them question our backasswards laws. I think it's important that we make an effort to know the facts about marijuana and be able to defend our point of view logically.
I'd also love to see some kind of local participation on 4/20...something as simple as driving with your lights on, or wearing green or something to signify that you support legalization. Given the power of the internet, if someone decided to start some kind of movement like this, it has the potential for the idea to reach enough people that a lot of people would participate. Again, it's not going to change laws immediately, but it will bring an awareness of the issue to people. (And it would let you spot fellow smokers! Heh.)