Diablo III Forum Rep Aguilar replied to a fan there won’t be a Diablo 3 demo at Dreamhack this year—the LAN party competition held in Sweden through November 27-30th. Blizzard will offer Starcraft II and Wrath of the Lich King Hands-on gameplay to attendees. You can find the Telia and Blizzard booth in Hall C right next to DreamArena. It’s a pity not to see Diablo 3 demo there. However, if you are going to be an attendee, you may ask the developers questions related to Diablo 3. Are you attending Dreamhack this year? Let us know.
And yes, members of the European community team will be there to answer your questions.
Sources: Dreamhack Official Site and Battle.net Diablo 3 Forums.