I'm torn on a dungeon finder. There's are positives like being able to find groups easier and negatives like cross-server DF's promote an anti-social personality that any WoW player knows about.
I vote no on the anti-social aspect of cross-server DF's but I vote yes for same-server DF's because the only reason I still have a WoW account active is because of the friends I've made from six years playing it. Many of those from 5 mans over the years or from guilds in endgame.
Cross-server DF's brings a nightmare that I hope Trion steers clear of.