FuzzieAlum, good point. The AEPhi chapter at Duke has all but disappeared, in part (I believe) because they do not participate in formal rush.
My chapter does a lot of COB rush, but our largest new member classes have always come from formal rush. We participated in fall formal rush, then held a COB rush week some time in the middle of fall semester and another early in the spring. (This will be changing as my campus is changing to deferred rush.) So we weren't constantly having rush events - but we were constantly rushing, in that we made ourselves very visible on campus and made an effort to get to know unaffiliated women. If someone approached one of us with an interest in joining, and a rush week wasn't coming up within the next month or so, we would strike while the iron was hot - we'd try to arrange for her to meet as many of the sisters as possible (take her to dinner, etc) and then vote on whether to bid her. We got some great sisters that way.