In Xero you've got something called a "Xero Network ID", which is an ID that you can give to other Xero users and they can link it to your contact record on their account, which means that invoices they raise are automatically posted in your Xero account without you having to lift a finger.
Now, you would have thought that Xero would do the same for their subscription invoices (i.e. automatically post them to your Xero account).
But no.....
Instead they send you one by email which you then have to post manually onto your Xero account. And they do that every ... single ... month.
If you ask them "why ?", you get an arrogant reply that along the lines of "we're too big to use Xero, so go away you silly little person".
But that doesn't answer the question. Xero is their dogfood. So even if they use Sage or whatever internally, surely it is not that difficult for them to build an integration so they can post their damn invoices to the customer's accounts.
Rant over. ;-)