Deadline has done a very good job following this whole Aereo "thing" from beginning to now. Here's a quick recap of what this is and why it is controversial:

The Barry Diller-backed service will stream local broadcast channels for free without the permission of those stations. At NAB, over-the-air broadcasters Fox, CBS, and Univision made the hilariously stupid threat to take their broadcast channels to pay-TV-only, which is actually a much worse move for them than to have a service that is basically IPTV-style Slingboxing:

It will stream programming from 28 over-the-air channels in Boston without their permission. (Aereo also has an agreement with Bloomberg Television to offer its pay TV channel.) Broadcasters in New York have already taken Aereo to court, alleging that it violates their copyrights. The company counters that it simply rents antennas, enabling subscribers to watch programming that’s already available to them for free. It adds that consumers also have the right to stream their content, much like they would if they bought a Slingbox.