Did your State have a Marijuana legalization bill on the ballot ? I know mine did.

Yep - Measure 64 on the California ballot.

Being Canadian, we are not voting. But I have a question.. IF medicinal  Marijuana is legal in one state, and a user goes to another state, is that person arrested?

It's been legal for a few years in Colorado, Washington, and Oregon.

But it's strictly a "cash only" business ... Because the businesses can't open bank accounts, since it's still illegal on a federal level.

I don't even want to think how taxes work.  The owners would have to declare it all as personal income - and can't write off any business expenses.