I saw this a few days ago and wrote craigslist as well. while very nice to have, I don't even need a nationwide search, even the ability to select a dozen or so regions would make it useful for the way it is supposed to be used (i.e. for local searches). I am willing to drive a couple hours for some of the items I look for, and in my area, there are at least a dozen craigslist search areas that fall within that distance. It's too much of a pain to cycle through all of them individually.
I would suspect that craigslist is getting their hardware pounded by these mega-search engines. There may even be some complaints from advertisers who don't want to risk getting scammed by someone wanting them to ship an item across the country.
Who knows what they are thinking.