It supports some javascript, but only a very small subset on the client. Depending on what functionality the website in question uses, sites may work perfectly, work partially, or not work at all. I don't want to have to worry about if the site I'm using is working correctly.No, it does support JavaScript, and even Ajax to a certain extent.
This link has some more information on what javascript is supported.
Opera is based in Norway, which has some of the strictest privacy laws in the world. Your data is safer at Opera than at most American companies, I would guess.
I don't care what privacy laws Norway has - there's no way I'm giving any of my financial information to a third party that has nothing to do with the initial transaction. That just gives thieves another avenue of attack to get my personal information. If I'm giving Amazon my credit card information, I want to be sure that Amazon is the only ones who get it. That way I have an avenue of recourse should my information get out.