We use Braintree's vault, and we use ActiveMerchant to access it. We wrote all of the recurring/billing/invoicing logic ourselves. Beyond the initial implementation, we've done one sweeping overhaul of the logic to make some improvements and simplify things after learning a lot from the first pass.
We built it in late 2008, and either the companies that handled recurring stuff didn't exist when we were building it, or we weren't aware of the ones that did. Otherwise, it's unlikely that we would have gone down this route. However, now that we have it, it is pretty nice to have control over every detail of how it works.
When we made the enhancements, we briefly considered switching to a provider for handling it, but given our existing infrastructure, it was actually easier for us to improve our own instead of migrating to another provider.