This happened on Wednesday evening at a newly opened skatepark in central Stockholm. My friend, Dave, was smoking some kind of herbal blend stuff that's meant to be a lot like cannabis, but isn't cannabis (that's as much as I know about it). It's legal here, either way. The skatepark is right under a big bridge, and as he was smoking it, some police officers passed overhead, smelt it (apparently it smells similar to cannabis) and looked down to see Dave smoking. They rushed down there and confronted Dave, who calmly showed them what he was smoking and said they could take it for analysis if they wanted to. Instead, they gave him two options: be arrested on suspicion of drug use or he could come with them to their van where he would do an on-the-spot urine test. Having not smoked weed in over a week, he chose the latter option and went with them.
They found 0.3 (unsure of what unit) of THC in his urine and he was handed a 2000SEK ($317) fine and has a "mark" for 5 years (get two marks and your fine doubles, or whatever). Apparently just having THC in your body in Sweden is a criminal offence. I was under the impression you had to possess some on you in person to get any kind of fine.