For the most part, everything you find in the Isles can be brought back to Tamriel. Custom armor and weapons make great souvenirs, and can be crafted from two new materials: amber and madness ore. For the alchemically inclined, 32 new ingredients will be available and will also freely pass customs back into Tamriel. Certain Isles-specific powers won't carry over, but would be useless in the "sane" world anyway. The Shivering Isles will be available from the beginning of the game, and creatures will scale in strength to better match the level of the player. If you've been looking for an excuse to start a new character, this just might be it.
To see the Isles in all their glory and be regaled with anecdotes from the developers, click the Movies tab above.
