I just started using Arq myself, and it's perfect for what I need. The Glacier backup is the killer feature. Tarsnap is really nice, but it would bankrupt me. I have 300+ gigs of photos and video (I have children and I'm a total tool with my camera, I know). That's $90 a month for Tarsnap vs $3 with Arq using Glacier. For $90/month it would probably be cheaper to rent a machine somewhere and just use rsync.