If you a traveling as a transfer passenger and you have second flight from Stockholm to country outside EU, so that check in and boarding pass could be obtained at the gates.
Free 30 minutes of wifi at airport. But if you are reading this tip, you probably already found it. Buses to city center are a lot cheaper than arlanda express train, takes about 45 minutes.
Stockholm City card, в которую входит много ништяков и транспорт тоже (чтоб добраться до города) продают в инфо-центре напротив выхода из терминала прилета.
Free wifi is available in T2 for a limited period of time... There are not a whole lot of restaurant options behind security in the terminal. However you can never go wrong with Starbucks
T5 is ok while T4 is a little run-down in places. All in all, decent airport. In T5, remember that there are multiple security check points as the "main one" can be very crowded.
Skip Joe & the Juice in the departure hall of Terminal 5, the coffee is bad and today's discomusic did not go down well either (see what I did there?).