Don't be discouraged by all the no hires you see on glassdoor. I was really worried when I first saw the number of people who got rejected but I think there are a lot of people who got offers who are afraid to post because of the NDA.
I found the interviews fairly easy. The only prep I did was reading through glassdoor questions. (Thanks guys!) If you've ever worked with user data and SQL, you'll require minimal prep for the interview. The SQL questions were not challenging but they are very picky about syntax (i.e. missing brackets, misspelled table names) even if the general concept has already been realized.