We have done a lot of movies over time, including home movies, and we've also put family pictures on ours, so that remote family members can access them. 1 TB goes by very fast.
The type of hard drive is important too--you want a hard drive that is optimized for NAS. I had the Western Digital green drives previously, and although they are good drives, they don't work well for this type of access. I like the WD red drives, in 2 or 3 TB.