"You can smoke and not feel like a criminal. It's really no different than having a beer or something. In fact, I think it's less dangerous," Calvin Lee told the local Kiro 7 television station.
The law made it legal for those over 21 to possess and use up to an ounce (28 grams) of marijuana. A number of US states have already legalized pot for medicinal purposes, but Washington is the first allowing it purely for fun.
Colorado residents approved a similar law last month, on the same day President Barack Obama was re-elected, but its pot lovers will have to wait until January 5 to light up with impunity.
But even while Washington's marijuana fans partied, the limits of the new law were underlined: the Space Needle gathering was technically illegal, since the new law allows only private, not public, consumption of weed.
Officers took no action, and the Seattle Police Department said that for the moment it will only issue verbal warnings, even though in theory they could impose $50 fines on those smoking marijuana on a street or in a public square.
Police drew praise for a blog -- which became an instant Internet hit -- taking a light-hearted approach to explaining exactly what is and isn't legal under the new law.
The "Marijwhatnow? A Guide to Legal Marijuana Use in Seattle" includes a link to a "Lord of the Rings" video clip entitled "The Finest Weed," showing wizard Gandalf blowing meditative smoke rings with Bilbo Baggins.
"In keeping with the spirit of (the new law), the department's going to give you a generous grace period to help you adjust to this brave, new, and maybe kinda stoned world we live in," wrote the police blogger.
"Does this mean you should flagrantly roll up a mega-spliff and light up in the middle of the street? No.
"But the police department believes that, under state law, you may responsibly get baked, order some pizzas and enjoy a Lord of the Rings marathon in the privacy of your own home, if you want to."
More broadly, the new Washington and Colorado laws run counter to US federal law, which still bans recreational use of marijuana across the country.
"Regardless of any changes in state law growing, selling or possessing any amount of marijuana remains illegal under federal law," noted the US Attorney's Office in Seattle.
Entrepreneurs are already eyeing the lucrative business opportunities provided by the advent of legal marijuana. Some have already dubbed them "ganja-preneurs."
"We're focused on Baby Boomers - basically wealthy Baby Boomers," said Jamen Shiveley, a former Microsoft executive who hopes to open as many as a couple of dozen pot shops.
"It's a $100 billion industry in search of a brand. Never in the history of capitalism -- forget America, in the world -- has such a giant vacuum existed," he told the King5 television station.
The state's financial chiefs are already rubbing their hands at the prospect of 25 percent tax revenues levied on legally sold marijuana, money which previously stayed strictly in the underground economy.
Washington's neighbor Oregon also held a referendum on legalizing recreational marijuana on November 6, but its residents rejected the proposal by 55 percent to 45 percent.