With Gamescon taking place right now in Germany, Trion has been pretty active releasing a couple articles or videos each day. IGN shared their hands-on experience at Gamescon. At the end of that article they stated that the developers' ultimate goal was to have enough dungeons that the player could reach maximum level by running each dungeon once. Either leveling is really fast or that's a heck of a lot of dungeons.
The videos coming out have been short teasers. The dungeon mentioned in the IGN article was Realm of the Fae, where you experience the four seasons as you progress through it. And it will be something we can experience early on, as it's a lower level dungeon. Rumors are that beta will begin in September. It's seriously getting harder for me to wait for Rift to release.