Hi. I have this. It does what is supposed to pretty well, but there are a few caveats.
As others have noted, most, if not nearly all, cable channels are encryted on most systems. You'll probably get your local broadcast channels (and digital sub channels) and a subset of other 'basic' channels in clear QAM. If you're a subscriber to anything higher than just 'basic' cable service, you're probably going to still want a cablebox (cable co, TiVo, Moxi), and use the HDHomeRun as a supplement.
There can be a bit of trial and error getting the clear cable channels set up, as many cable systems fail to provide an easy to decipher listing of the QAM frequencies of their signal. The HDHomeRun will scan the frequencies and find the clear signals, but you may have to set which station it is manually. You can download a database of channels from the SiliconDust servers, but it's only as accurate as prior users information. And cable companies can and do switch QAM frequencies without prior notice or providing the new frequency allocations.
That said, the HDHomerun does it's job of tuning and streaming signals to your HTPC virtually flawlessly.
Of Course, if you're OTA only, none of those limitations matter than much.
And one final and valuable note about the product: each tuner can be set to a different service--meaning one can be for clear QAM cable, and the other OTA.