This is really good info in this thread and I'm interested in using bitcoin, but is there anyone who had a bad experience / loss of funds?
You can definitely lose all your bitcoin if you have your wallet saved on a local hard drive and the hard drive crashes, but it's actually really easy to back up and restore your wallet so there's no excuse to not do so. When you create a wallet with a program like Multibit, it will give you a short passphrase of some random plaintext words that you're supposed to write down on a sheet of paper, like "umbrella baboon window..." etc. You can then put that sheet of paper in a safe deposit box in real life. If your hard drive crashes, you can recreate your wallet from any computer using only that passphrase.
There is a long thread on bitcointalk.org about people who have lost bitcoins in real life and it definitely happens. However, like all data loss stories, it's when people don't make backups and forget their password or their laptop catches fire and they didn't write down their wallet words. If you take some reasonable precautions like backing up your wallet, it's not something to be worried about.
Regarding bad experiences, I once had ACR not credit me for about ~$20 worth of a bitcoin deposit. It was only that one time, though, and I think it was general idiocy and ignorance on their part as opposed to them trying to scam me out of $20. I never did get my money back, though. Most of the sites that use bitcoin (everywhere but bitcoin-only sites) don't know anything about bitcoin, they just have a bitcoin payment processor just like they have a
visa payment processor and a Neteller payment processor and a
skrill payment processor. They are not willing to go through a public-domain bitcoin transaction history with you where you might show them the error of their ways, they just know what their payment processor told them.