seems to depend on the airport. At BOS, I never get stamped. Nor at JFK. At LAX, once out of three times. MIA, nope. YYZ's pre-boarding clearance, never (though last time they stamped my boarding pass).

At my hometown airport ORD, they always stamp incoming.

Like MBS PremExec, I have a cool non-US US immigration stamp from Dublin, where you pre-clear as well (didn't know they had that in Aruba now).

Doesn't it seem like the US immigration stamps should look more interesting? I mean, the Chicago ones don't even say "United States of America" or "USA" anywhere on them. I guess the UK is similar (just the name of the entry point).