I've just started on a free trial of
www.footnote.com
I used the "Advanced Search" to search for various names in my tree who emigrated to the US or were born there, and all I've found are records that I already had from elsewhere (ancestry, familysearch etc) and I was about to give it up as a bad job when I had another look at the front page and decided to try searching some of the databases separately.
So I tried the newspapers database and I remembered that the death notice for my 2xg-grandfather that was printed in the English papers in 1917 had a bit at the end saying "American papers, please copy". So I thought I might as well see whether it did actually appear in any American papers, and put his name in the "keywords" search. I haven't found the death notice yet, but I have found something much more interesting! A personal ad from 6 months after his death, printed in the Chicago Tribune, asking his daughter (my g-grandmother) to contact a company in London (solicitors, I think) where she will hear something to her advantage.
I'd always wondered why the death notice was to be copied to the US papers as I haven't found any of his close relatives emigrating to or travelling to America. My g-grandmother was in Belfast the year before her father died, and she died in Belfast the year after his death, and I would assume stayed in Belfast between those two dates. So it looks as though her father (who died in London) didn't know where she had gone. No address was given for her in his will, but I didn't know till now whether that was because they didn't have an address for her.
Now looking through for more stuff. The ad seems to have appeared several times.