Agreed. I experienced a big. Bug the other day that appeared like it deleted all my notes on my iPad and online and this caused me to finally bite-the-bullet and move my notes to Evernote from my offline iPhone for fear of never being able to access them again.
Was a painful upgrade experience (and the bug resolved itself in 24 hours), but I've suffered similar sync bugs over my time with Simplenote over the past 2 years and I didn't feel safe with the service anymore.
We've had a few growing pains, particularly with 3rd-party apps. We're working with developers to move them to our latest API. If you ever encounter problems, you can email us at support@simplenoteapp.com and we'll do our best to help you out.
Sadly, I too found it unusably buggy. I reported a number of them. Some were fixed, some weren't. Their support response times were great and I really hoped they could get it working smoothly but after a year I was still having issues and it was not to be. Shame because I loved the simplicity.