Not really. Financial transactions are really almost never implemented with database transactions.

A lot of people truly don't understand how financial companies do stuff. Hell, Financial companies are ones who are adopting Mongo and the like themselves. We all assume it's one way, when it's actually done another....

They're really only doing that for hipster cred. That way they can easily write articles titled "How I made (really simple/trivial application) with (really fledgling technology)" such as "how I made a twitter client with node.js" or "how I put 2 sprites on the screen with webgl" or "how I managed 2tps with java".

We know all financial companies use databases running on tandem or tuxedo. But that's not cool sounding. How are they supposed to get fun jobs doing nothing with catered lunches? HOW, HOW I ASK!

What financial companies are adopting Mongo for accounting/customer transaction storage?

I've heard of somewhere like ADP using it but they are using it as an analytics database, not for actual payroll processing.

I'd love for you to expound on this point. I'm curious, what are they doing?

What is crazy is people claiming a bank uses a transactional database for their financial transaction processing or that all parts of that system are "ACID". Both are false. Don't like MongoDB? Fair enough, it isn't great. But the tech banks use is a lot closer to MongoDB's persistence model than it is to your typical RDBMS.