N.B.—My team probably ranked in the top five for pager pain metrics. I've seen the histograms, and there is a long tail. You'll likely find yourself in a team with far less pager pain, but be warned that it can be bad.
Yes, you have to carry a pager. Yes, it can be hell. You will invariably try to go to a pub one hour before your rotation ends only to be paged into an event that requires a conference call with multiple VPs and on-edge datacenter engineers. You may go to bed at 1 AM Sunday night, be paged at 5 AM Monday morning and not stop firefighting until 2 AM Tuesday. It can be draining.
People say Amazon never ships a version two of anything, and I think this is the reason why. Asking your educated thought workers to sit around doing menial "keep the stack running" tasks can be a pain, and the small team sizes are great and all, but you'll find yourself wishing for more people to share the pager pain; misery loves company.
At one point my project entered a dark phase in which all feature development tasks were superseded by the need to just keep the service up and running. Hacks and kludges were put in place to reduce the load and extreme measures were taken to keep us up and running. In retrospect, our project was characteristically different from other web services and this sort of thing was predictable, but we didn't get ahead of the problem quickly enough. One tends to blame management when these things happen; saying "we'll take the technical debt and put it on the backlog for now" one too many times can result in one hell of a lot of interest to pay off.
The whole period seemed like hell when it was happening; a team member switched teams, the intern went back to college, the managers did a nice little switcharoo, we had three developers to actually code. But it passed. And I got an offer with another team with essentially no oncall rotation and whose work I really admired. I didn't take it because I knew I'd soon leave the company due to a cross-country move (I didn't want to join a brand new team for only two months), but the thought crossed my mind.
So if you have a needy family, enjoy sleeping, or can't bear the thought of a pager, maybe Amazon is not for you. If you're willing to look past that in order to work at a company that actually ships products (rather than having them always in beta or research), I say the pain outweighs the gain.