that's normal! you will always get that message in the UI if you kill siad.
another thing i remember is that i could sometimes trigger it if i copied files around. especially the large consensus.db file. I could just copy-paste it to another folder on that disk and then the disk would crash, also without Sia running. That's why i first thought it's a Sia problem but later i saw that it also happens with other files and then i concluded it's a disk problem.
I guess it's best to just run siad in the command window and see if you get some error message. Maybe also delete all the *.log files first so that new ones will be created. Then it's easier to see if there are any messages in the logs.
The address changing is normal; the UI generates a new address for you when you click the 'Receive' button, to discourage address reuse and encourage anonymity. You can see all your addresses by typing 'wallet addresses' in the Terminal plugin. You will always be able to receive coins at an address you generate with 'Receive Siacoin'.
@juandfacundo a lot of the early hosts are using drives they have already purchased or just have lying around, which means that they can make money while still offering very low prices. As the network matures, and as the redundancy requirement is lowered, we will probably see the payout settle between $1 and $2 per month per TB for hosts. A 12-24 month ROI for hosts seems pretty reasonable - most drives last longer than that, which means that over the course of 3 years you should be able to make 50% returns, which is pretty significant compared to the growth of the stock market.
Time will tell. Sia is a competitive platform, which means the best/cheapest/strongest hosts will make money, and the rest will probably be out-competed. It's too early to know exactly where the optimal price will fall.