Craigslist has never sued anyone for reimplementing their 'idea'.

Craigslist didn't 'steal' the classifieds business, I recall no point in time which I could find the classifieds in my news paper copied verbatim onto craigslist.

Craigslist offered a solution which was superior to newspapers and built a business around it.

As to who holds copyright on the data that's a question for the courts that is currently undecided, if it was cut and dried as to who held copyright on the the data then summary judgement would have already been filed.

I don't think craigslist holds exclusive copyright on the data so in my mind they may lack standing as whether 3taps is allowed to use the data becomes an issue between 3taps and millions of other users, perhaps a class action suit is more appropriate.