I have the latest Mavericks and Alfred and use Alfred's find and open without trouble but 'in' isn't working. You'd expect 'in' to use find then open then a search for the string, but 'in' doesn't even give the same found list as find and open; and 'in' sometimes can't find files at all when find and open can. The function 'in' seems to work sometimes, and when it does you'd expect to be shown the document page with the found string highlighted but it doesn't do this - what it does is to open the document at the page it was at when it was last closed. Also, 'in' doesn't like to find anything containing numbers.
The 'in' function.