Comes with being a startup, but not as much support is available to ramp up new employees, and they are largely responsible for reaching out to busy coworkers to get up to speed. As a new grad, I felt unprepared and overwhelmed by the responsiblity and "real production issues" that I had to tackle within my first few weeks. I would say it was a great learning experience, though, for those who can handle working under pressure.
Although Mountain View is considered "HQ", much of the engineering team is centered in Poland and operates in that timezone. As a result, you will most likely have to attend at the very least biweekly meetings at either somewhat late night (22:00) or worse, very early morning (06:00, not me thankfully). Also, the agile software development process is hindered by requiring approvals from people on the other side of the world.
Very agile work environment, priorities and feature specifications change often to accomodate prospects' needs, or percieved needs. This can be somewhat frustrating when spending a lot of time and developmental resources creating features that are not even used (although it speaks to management's transparency that we know that they're not being used).
Engineering is understaffed, more developers would be nice, but more importantly, we are in need for product managers in more than one area.
A caveat to unlimited PTO/flexible hours and the small team, you may be required to do urgent tasks outside work hours/during PTO in emergencies.