As mentioned in all previous comments on Karin's apartment, this is a perfect place if you want to visit Stockholm.
Localisation is very convenient (100m from Arlanda airport bus station), near metro station and 15mn walking distance from the very center.
The apartment is great : you really feel like home (or like the home you would dream to have :-)).
Absolutely no hesitation if you are looking for a nice place to stay in Stockholm.