A few years ago I was briefly part of the test team for Pixel Plow render farm to test Terragen rendering service.
Unfortunately ever since I haven't had time or decent projects to make use of the service as a customer.
Until now

I must say it improved a LOT since.
Submitting your jobSubmitting is easy as pie.
First export your TG project using the "export gathered project" functionality.
In the Pixel Plow agent choose the "...(gathered).tgd" as your to be rendered project.
All other steps are self-explanatory.
The client ZIP's the project files and sends it to the farm using an encrypted tunnel.
During submitting you can already state your maximum budget.
Should you make a mistake with the online calculator
http://www.pixelplow.net/pricing/ then you can avoid exceedingly high costs by simply stating that you don't want to spend more than X dollars. Great!
Be aware that mistakes are easily made and usually on the user's end.
Especially with larger sequences the render time per frame can differ quite much and thus it's difficult to estimate the average render time per frame.
If you'd like to know, you would actually need to render the sequence yourself first

Allowing for a maximum budget is a nice fail-safe and a very customer-friendly service.
Delivery of your jobBack in the time, when testing, my only issue with the service was that some frames weren't delivered.
The problems were difficult to identify and to resolve as they were on both ends.
In the end it worked well enough and it seemed to be machine-specific to my case.
At the moment the client seems more intelligent and flexible on the 'availability' of the customer's connection.
File delivery is being checked on both ends by the client and should the render job be finished on the farm, but not delivered on your system, then you will receive a notification by e-mail.
Next time you start the client it will automatically download the remaining frames.
So, if you should ever have a system which somehow doesn't 'like' the client, then your render job will not be lost.
It's a great improvement.
In the end you will receive a notification that the job has been finished and delivered.
Your account is connected with your Credit Card and payment is fully automated.
ConclusionIn the latter lies a bit of 'risk' for the customer.
It's too easy now

Submitting a job, controlling priority and your budget all go very smoothly and quickly.
Before you know you submit another job

I had a short 48 frame sequence of ~200 minutes per frame, which equals 6.7 days of rendering on my 3.4 Ghz HT CPU.
It cost me $12.10 to render on Pixel Plow.
Absolutely worth it.