It has been known for quite some time that flickr is really not a good place to host your photos because their privacy and security is pretty much non existent. I have read many many many stories about people having photos being "stolen" from their account and used in advertising or for other means. I don't recall the name of the software, but there is one out there that business can purchase to make searching for images on flickr much easier. This software is (at least when I first read about it well over a year ago) something that flickr knows about and hasn't done anything about. Maybe they have changed over the last year, but I haven't heard anything.
I have heard of Virgin Mobile, the Cleveland Post Dispatch, and Toyota taking people's photos to use for advertising and not contacting the photographer.
This article about using Flickr photos to decorate your home was in the NYTimes last year. (the NYTimes did have to post another article about legal issues to cover their *** though).
This is an older article that I came across about a year and a half ago.
http://www.jmg-galleries.com/blog/2008/07/07/how-every-flickr-photo-ended-up-on-sale-this-weekend/
Considering I'm still hearing stories of people stealing images off flickr, its obvious that things over at flickr have not changed.
Now with pretty much every photo hosting site you can have people "steal" your photos, but try doing a google search for stealing flickr photos and see what kind of results you get, then do the same for zenfolio and smugmug. HUGE difference. I have removed all my photos on flickr.