1) Privacy: Yes, this a privacy risk. 23andMe is fundamentally an IT company, and IT companies mess up. But I am confident that within 10-15 years genetic information is going to be pretty easy to get anyhow. Your data will be in too many places for any expectation of privacy.
2) Cost/worth it: That is dependent on your income. If you are willing to spend $100 on a nice meal, I think $100 for 1 million markers is an excellent proposition. The markers never depreciate, though in the near future you will you get sequence data which will supersede them.