Everybody is dying for more integration in Google products, so how about some cross-gadget interaction? Here's a few scenarios...

I want to to share an RSS story. Drag from Reader into Gmail.

I want to create an appointment from an e-mail. Drag from Gmail into Calendar.

I want to e-mail some photos. Drag from Picasa Web into Gmail.

As far as I know, this isn't currently possible. No doubt the XML schema would need to be changed drastically, to accommodate gadget developers. Yet, it would open a new window of opportunity. Would anyone else find this useful?

Of course.
Correct me if i'm wrong but Google is working on tthese interaction already.
It's just a matter of time.
But as Joe said, it's important.

Mambo, you can already create an appointment from Gmail.

I sent myself a test email that read:
   "Your appointment is scheduled for July 2, 2007 at 3pm."

Gmail will then have an "Add to Calendar" link to the right of the email message. This allows you to add the event to Calendar.

http://farm2.static.flickr.com/1263/633517138_8901d9a6f0.jpg?v=0

Sorry, I don't think I made myself clear enough...

I mean to have drag-and-drop functionality between iGoogle's modules, removing the need to even open the web app.

I'm not sure it would work cross-browser/tab window on all browsers (depends on each browser, I guess).

A way Google could implement such a system would be for a user to drag a link to the Google nav bar. Say I'm on iGoogle, I just drag an Feed gadget to the "Reader" link on the Nav bar and Google asks if you want to add the feed to Reader and does it automatically.

That would be quite nice. But seeing as iGoogle is the only Google product (or feature, as Google calls it) that has Drag and drop, it's very doubtful. iGoogle isn't fully AJAX which adds another point to the "Just a dream" column. Any page update/settings save/tab change is actually done by reloading the page and not AJAX.