SALARY IS HORRID. Prepare to be paid absolute crap if you work with this company, and don't be surprised if you notice things like how they change their offer before onboarding you, trick you into accepting a different title with lower pay when you actually come on as the higher title you were interviewed for in the first place, and gouge the normal salaries paid for people who actually work for the partner company, leaving you beans. The position I work now is normally paid upon entry about $30k more than Milestone is paying me, as an example, so they are making insane amounts of money off of me right now.
HR IS USELESS. Somehow, simple administrative items like listing open positions with appropriate titles and correct job descriptions is something that eludes those within Milestone, and good luck actually starting a position anytime soon after it's offered to you. If you have questions about how anything works on the HR end, expect no answer or weird answers or wrong answers, because it seems like the whole department is just winging it all the time.
MOST PROJECTS ARE EXTREMELY DISORGANIZED. A great example of this is the Google project, which I wouldn't be surprised if Milestone got fired from within the next year because of the insane level of disorganization and ridiculously horrid management. It's just really really bad, at every single angle, and no one cares or tries to really fix it. Other projects have similar issues, but I haven't been to all of the projects, so I can't speak for all of them.
THE HIRING BAR IS EXTREMELY LOW. It's not terribly difficult to get into this company. It's also not terribly difficult to get walked out for any reason they decide at any time. For the competent, it's incredibly frustrating to have utterly useless team members coming and going.
THERE IS NO UPWARD MOBILITY. Seriously. Milestone is a good place to start if you are new to the work world or even to the Bay Area, but it's not a place to stay for long.