I ALWAYS do that on the return segment. Even though I am ticketed on the cheap $158 IAH - JFK segment, I request for a standby to EWR. Sometimes, the only flip to this is I have to give up a confirmed first class upgraded seat to a waiting game on the EWR flight. But last week, i was wow'ed. I had been upgraded first class on my $158 fare IAH - JFK flight, I did a stand-by for the EWR flight, and that equip was a 767-200 with BusinessFirst seating which I snagged!