SPOILERS: Photos of the Set at Lower Hutt - Updated 5/17 - Exclusive Photos of Imladris?!
5/17 Update: Susan also chimed in, saying, "It is definitely a Rings set -- the (in)famous "Jamb" sign is present! One item of interest -- this set is right next to the local railway line -- hope they've got timetables of the suburban passenger trains (mainly daytime) and the freight trains (night-time)!!"
Also, "Priam" sent an email in which he used his deductive capabilities to discern the set as Rivendall/Imladris. Here's what he said:
It seems that, what with a pony with an unusually large pommel and cantel, that one of the hobbits shall be riding it: what with the imaging technique reportedly used on the hobbits, it would look weird if Aragorn's pommel looked the same size compared to him as Frodo's pommel...
That leaves Bill the Pony and the several ponies used between Hobbiton and Bree. Large crane-mounted cameras indicate panoramic shots, though they can be used simply for their steadycam applications as well (for converse while mounted). I DO NOT KNOW ABOUT THE AREA, but it seems it could be either the area between Hobbiton an Bree or southern Eregion (near Moria). However, the source mentioned "strange gear" on the pony, which could be ANY-thing having to do with Middle-earth, but hints at Elven stuff.
Having a multitude of cars there hints at lots of peeps; and a scene at or leaving Imladris would make sense: you need lots of extra elves, and as elves are high-maintenence for a director (make-up etc.) I can conclude that...
The scene being developed was leaving or at least in Imladris.