I haven't checked with them, but I'm really surprised that no one else here has any comments about this. I was having a problem thinking of something generic to link to (instead of the PSAs) and this sounds perfect to me.
Beggars, sounds like a really good idea. There may be formatting issues - for example if you are serving skyscrapers, it will be difficult to make it work. But with leaderboards it could be a nice fit.
I was experimenting with this today. It works fine except for one formatting issue. Let's say you are running something like a big AdSense leaderboard ad. When the alternate Google search box is displayed it's surrounded by the huge white space allocated for the leaderboard. It's dwarfed by the white space.
It seems like there should be a way to bypass the leaderboard space when you are displaying alternate ads. Any suggestions?