In the interest of playing devil's advocate, I've only ever heard of one case that makes any kind of sense. Some local and state govs are using emminent domain to clear out "blighted neighborhoods", those places so drug and crime infested that the cops spend all their time there, if they'll go there at all.
When I bought my house, we learned too late that the "bargain" we landed was owing to a trailer park two blocks over (and out of sight of the property) was basically East Pasco County's personal meth lab. The cops were down there every day and night, including the occasional overhead chopper search.
In our case, the county didn't use imminent domain. They raided the place, busted some bad guys, and condemned the whole park and ordered everyone out. The slum lord that owned it couldn't afford the repairs, so he sold it to a developer. The developer cleared it, then the housing bubble popped, and it's sat untouched, trailer-free, for over a year.
There's alot of debate about this practice, and I'll let wiser heads than mine hammer out the details. I'm content that although cops still prowl my neighborhood at times, at least we get no more fly-overs. The choppers upset my great dane.
TM