Today, Colorado embarks on what many people feel is a risky social experiment. The doors of 136 medical marijuana stores will open for the legal sale of pot for recreational use.  No doctor recommendation is needed. You will be able to walk in, make your selection of product, show your ID to establish your age and residency - and that's it.

Both Colorado and Washington state saw successful ballot initiatives on legalizing pot last year.

What will this mean for Colorado and the nation? State governments will be watching very carefully. The legal sale of pot is expected to top half a billion dollars the first year, with $67 million of that going to the state in taxes. That's not small change, but might legalized pot create its own set of problems?

The Feds say they won't enforce national laws against pot in states where it has been legalized, but that decision can be reversed by a new administration or new facts that come to light. One of Washington's big worries is that out of state drug dealers will travel to Colorado, going from store to store, purchasing the one ounce limit at each establishment, then driiving home with a trunkful of weed. Buying legal pot takes a lot of the hassle and danger out of drug dealing. No one knows what that means for the street price elsewhere.

There is also the concern that kids under 21 years old will still be able to get some weed, regardless of efforts to keep it out of their hands. And there may be a large spike in drugged driving charges and a consequent rise in accidents and highway deaths.

So legalizing pot may be a feel good measure that seems to benefit both the people and the state. But these and other unintended consequences may rain on Colorado's pot parade and give other states pauise before they legalize marijuana.