I use Premier Pro CS5, which takes the native GoPro footage like a champ. I drop it into a 60 fps timeline (actually 59.94, but whatever) and for slowmo just set it to play at 50%, which makes the frames go at 30 fps- it makes each individual frame play for 2 frames in the timeline, but when you export in 30fps, it makes no difference.
Only thing is that for this to work you must make sure frame blending is turned off when you export- that way, instead of comibining two 60fps frames to make one 30fps frame, it just throws out every other 60fps frame while exporting. Takes longer to render, but that's downtime I'm spending on NS anyway.