Zeitgeist can already make users lives really easy (see my last Awn + Zeitgeist post), but we don't have to stop there, one of things I'd really like to see would be if applications helped us with this - if the apps expose which URI they are currently working with (which file is currently open / web page currently viewed / ...) we can make very precise queries as to which other files (or contacts, web pages, applications etc.) are related to this URI.
As everyone likes examples imagine that you're working with a spreadsheet and zeitgeist knows that the last time you were working with it you were checking www.sitewithstats.com, had last_years_report.pdf open and were talking to xyz. Therefore it will provide you these options in some kind of menu (or dock / indicator / windicator). Wouldn't it be great?
To make this possible I suggest new X property for windows (let's say it'd be "_NET_WM_CURRENT_URI") and the only thing required by the apps is to set this property when a file is opened and update it when appropriate. If people like this idea I can prepare a patch for gdk (adding gdk_window_set_current_uri_hint) and libwnck (which would expose the property for pagers). Or perhaps there is already something similar what I missed?