Originally Posted by Tomas E

Then you were definitely unlucky. I've never been more than around 10 min late with Arlanda Express (and if there's a delay of more than 5 min you get a voucher for a new ticket, so they don't plan on being 5 min late very often). AFAIK, they only have shared tracks for the short final stretch out to Arlanda, that's why they are able to be fast. FlyingMoose was this very recently, with full service restored, or when they were operating a reduced schedule on one track past the site where they derailed this summer, with full repairs taking quite some time? My guess would be that security stops due to persons (I'd say "idiots"...) in the track area (stopping trains on all tracks until they've been cleared) would be more common than broken down trains on the short stretch of shared tracks.
Admittedly, I use the commuter train more often than Arlanda Express, so I guess that on average I've used it once every 1-2 months in recent years.