Meta

Almost unbelievable autonomy and trust are given to engineers; most projects are bottom-up versus top-down.

Big, interesting projects are everywhere; if someone is bored at work, they're not trying very hard.

The caliber of peers is extremely high.

For the most part, there is rapid adoption (and often creation, e.g., a VM for PHP) of new technologies.

Many (though not all) engineers tend to work lots of hours, mostly because they just enjoy what they're doing. If this isn't necessarily your lifestyle, you may feel like you're not "keeping up". This is really all in the eye of the beholder, though, as there are many engineers who are very effective and productive and use that to work more limited hours so that they can enjoy family/non-work activities.

Most teams have rotating on-call rotations, wherein the engineer must be available to be paged 24 hours a day (typically for a period of a week) to respond to issues with their product or service. This is more of a burden for some teams than others (e.g., a core piece of infrastructure vs. a little-used feature). This isn't particularly fun.

Rapid pace of product change means it can be a challenging place to be in infrastructure. This isn't necessarily bad, but it does require flexibility in planning and mindset, particularly if you come from a company where software releases are measured in months or years.