Churches of Christ frequently use shape notes in hymnals as a sight-reading aid, and they almost all sing a capella, but the style and arrangements are usually very different than what you'll hear with Sacred Harp-- more melody-focused, like a conventional choral style.

(I grew up in the Church of Christ and what I've heard of Sacred Harp sounds pretty chaotic to my ear, even arrangements of hymns I know well. But it's an interesting sound, and it's probably fun to participate in.)