I had several domains with a registrar that specialized in the .us when that was made available a couple years back. They came up for renewal, I paid right at the very last minute and thought all was well until I was not able to log in to my account on their system. They went out (or thrown out) of the registrar business and did not renew my domains, but kept my money. I tried calling but the voice mailbox was full, apparently I wasn't the only one getting screwed.
These guys sucked from the beginning and I wasn't about to be shafted, so I did some background checking and found a number and called it. I got in touch with someone and demanded a refund. But a day later I contested the charges to my credit card and eventually got the credit and at least I got the satisfaction that they were probably charged a fee for the contested charges.
I ended up losing several domain names that went into redemption at enom - where all the rest of my domains ended up at. It sucked cause I lost a couple really good keyword filled domains.