Second this. Just found this thread and was wondering if anybody else started using their service. Started off using it for my wife's products and bulk shipping. Signed up from my end as well to take advantage of savings.
Here are the advantages I see from using PirateShip so far:
1) Convenience. Every single shipment from my end whether domestic or outside of the US has been sent out without even having to step foot in a nearby post office. Purchased the labels, pack and stick the label on from home, and have the mailman take it. PirateShip will even allow you to digitally fill in Customs Declarations forms that have to be attached to an international shipment. Normally you have to grab those at the post office, fill them out by hand, make sure you press hard enough for the carbon paper to do its job, then wait in line to send it out.
2) Savings. As
@Parrothedd mentioned, the savings add up. I also came across a tip on their website to not always send in MFRB or LFRB. If the recipient is in a nearby Zone, you're saving money by sending it in your own box. Perfect example are the three racks going to someone via a giveaway I ran. They're going to Vegas. Just calculated the cost on PirateShip in my own box measuring 8x8x8. Cost is just a shade over $8 compared to a MFRB retail cost of $15.05 or even the discounted PirateShip rate of $13.20.
3) No delivery problems due to legibility. Everything is printed right on the label as it's entered into the system. I've gone a step further due to my wife's online business and print the labels using a thermal printer. Print, stick, go.
4) It's free. You can't say no to saving money for free?! No catches. Entirely free service to use.