I did it in 2012, when it was 4 degrees, stormwinds and heavy rain... Other years it has been 30 degrees and sunshine so it depends. Most years I will say the weather is "average" for this time of the year. Weather in Sweden is about the same as in the UK.
I have also been out as a spectator many times during the marathon and with the race taking place on a saturday afternoon in late may/early june crowds are usually good.
The course is on the tougher side for being a city marathon and you have to cross a large bridge twice so probably no PB in this race. The organization is, as you may expect in northern Europe, very good.
A couple of days ago I came to think about an infamous cheating that happened during the Vienna marathon, probably sometime in the 90's: Some runners had discovered that it was possible to cut off a big part of the course by travelling on the subway between two stations. On race day, it was several runners who did this and finished in really good times. But they got caught and the story was spread over the world by the media. I remember the incident was widely reported in the Swedish press, but now when I try to search online I find no information about it. Is there anyone else who remember this?