Unfortunately, it doesn't replace cable, since many channels are not available over-the-air, but it does let me use my HdHomeRun (with two tuners) to record (in HD) any of the major networks, leaving the single-tuner cable box free for cable-only channels.
The antenna is now much more reliable than the cable box. The box appears to restart in the middle of the night sometimes, even if it's in the middle of recording a show. And occasionally, seemingly with no rhyme or reason, the firewire output for a particular program is encrypted, which makes the recording fail. The antenna has neither of those issues.