PS if you are flying into Arlanda the train is pricey. If there are two of you, you may as well take a cab..
Also the bus is also not too bad cost wise and not as bad as it sounds. It has free wifi.
Not spent too much time in Stockholm - 1 night last time, did the old Town/Royal palace, went to Skydome (which was OK, not a must do though) and ended up eating at the Hard Rock café
Stayed with relatives after that.