I'm thinking from a startup's pricing standpoint, not necessarily from the customer's perspective. As someone starting a web service does it make sense? Contrast with basecamp's $1.60 per project on basic and $0.99 per project on premium.

My opinion is Basecamp's pricing is much more stable, and makes sense, while chargify still needs to figure things out.

Also, I've been using Google Checkout for my startup's billing so far and it works reliably. They do have a subscriptions api and it works well. I absolutely agree billing systems do take a huge amount of time to make, and it'd be silly to concentrate on them instead of the product.