Me being the audio snob that I am, I was using SongTowers, which was awesome. However, in my new home I've found that I enjoy the rear set of SongTowers as computer speakers, so I can listen to great tunes and work.
So I will probably try and pick up a pair of SongSurrounds if I ever get money (which I likely will not), or I will use my old Rocket 250MkII's.
I've been to Swerd's house and he uses just plain run of the mill cheapo surround speakers, and they sound fine with his SongTowers. The rears really don't see much action, how much fidelity do you get playing a "whoosh"?
The only thing would be if multichannel music was your thing, you'd probably want as good a speaker as you could afford.