The conference is held at Electrum in Kista, just north of Stockholm. There are entrances to Electrum from Isafjordsgatan 22 (delivery and taxi) 26 (parking), and Kistagången 15 (by foot from either Kista Centrum or Helenelund station).
You can take a taxi from the airport to downtown for 250-300 SEK. The taxi stop at the airport is regulated so make sure you get help from an attendant (who works for the airport).
You can also take the airport shuttle ("Flygbuss") from Arlanda, which costs 50 SEK for a one-way trip. Take the shuttle that goes towards "Barkarby". The shuttle starts from terminal 5 and then picks up passengers at terminals 4 and 2. The shuttle leaves every 30 minutes starting at 07:05 (AM) until 9:35 (AM), and then starts again at 15:05 until 18:05. The ride takes approximately 30-35 minutes. Note: the Barkarby Shuttle does not run on weekends!
When the "Barkarby" shuttle is not running, you can take the "Brommaplan" shuttle, which stops in Kista Centrum, approximately 6 minutes walk from Electrum. The Brommaplan shuttle leaves every 30 minutes starting at 10:20 (AM) until 14:50, and 18:50 until 21:20, with two late departures at 22:00 and 23:00. The Barkarby Shuttle takes approx. 25 minutes to Kista. On weekends the evening departures are a little different, with departures after 17:50 being: 18:50, 19:50, 21:00, 22:00, and 23:00.
(Note: the "Brommaplan" shuttle runs at other times than those give, but does not stop at Kista Centrum. For example, the 15:20 Brommaplan bus does not stop at Kista Centrum - instead you should take the 15:05 or 15:35 Barkarby bus.)
You can either take the subway ("Tunnelbana") to Kista Centrum, the blue line. Best exit is from the rear of the train (i.e. the wagon closest to Stockholm). Take a left after entering Kista Centrum (a shopping complex), continue straight. Electrum is the first large building after you cross the bridge (approximately 6 minutes from the subway station. Departures are frequent.
Alternatively, you can take the urban train ("Pendeltag") towards Marsta. It leaves the main railway station 16 and 46 minutes after every hour, taking approximately 12 minutes to reach Helenelund station. There is only one exit, take a right after coming out into the tunnel under the station. "Follow the crowd" from there, basically straight ahead towards Kista Centrum. You will pass a large building on the right, the last building immediately before crossing a bridge (but after walking *under* several). It is a 10-minute walk.