They are definately worth it. They are one of those mods that don't make a massive difference by their selves, but it certianly adds up when you start doing other things like underdrive pullies and a driveshaft.
Bamachips dynotuned a set to the tune of 6-10HP all across the board, if I remember correctly.
You do have to get them through Steeda now, Ford can't sell theirs' anymore. By the way, don't forget to get a tune for them when you get them.