the idea is that you set up an alert for topics that interest you. Then when google sends you stuff, you have instant content for you blog. Unless you rewrite it, it will be duplicate content, of course, so about as much use as a chocolate teapot. You can even automate the process if you want to fill your blog with dupe stuff - there's a thread about it around here somewhere - basically set your gmail to forward to your secret blogspot address, that kind of thing.
I use alerts for all my sites and competitors, adding comments whenever applicable. It works especially good with the holiday sites, http://www.invitations-shoppe.com and http://www.holiday-invitations.com
So getting idea from Google Alert and Rewriting it at our own is not duplicate content. is it ok ! what do you say.
It can be google for finding out who is talking about you, or your site... also, pop in a google alert for 2 sentances of your content, within " and " - so you can find out if anyine is duplicating your content ;-)