Ok, tested this against Photoshop's Content-Aware Fill on some same pictures.
I found Inpaint's interface to be pretty dreadful. It's looks like it was barely ported over from Windows to Mac. Aside from those terrible aesthetic issues, it also doesn't use standard Mac shortcuts for the tools either.
For example, command + or - doesn't zoom in & out. It says it's supposed to if you look under "View" and observe the shortcuts, but pressing those keys does nothing so I'm forced to click the clunky icons to zoom in and out that look like they are from Windows XP hell (saving is with a an old 3.5 floppy disk icon).
Also zooming happens in much larger steps than Photoshop, so don't expect to zoom to an ideal size to fit perfectly in your window/display unless you get lucky.
You can adjust the size of the brush to select the area you want to erase with the content aware fill with a sliding dot on a line, but there's no feedback to how large or small the brush is exactly until you use it. Super-clunk.
Performance. Sadly, you also get clunkier, blockier results than Photoshop's content-aware fill which is smoother on edges.
I had hoped using the guidelines to define edges would have given Inpaint "the edge" over Photoshop in results, but in my testing it was just more steps to get the same result but clunkier and less natural results than Photoshop, so that was a disappointment.
I was hoping in the end this would be a scrappy alternative to Photoshop's content-aware fill with better results with more custom tools (like the Guide Lines), but this hasn't been my experience.
On HUGE plus side, this thing is only 20 bucks and while the results aren't as natural/smooth as you get with Photoshop, it definitely works and if you don't mind a little more cloning/retouching to fix up its results than you would have to do with Photoshop's results then this a great alternative to spending a bunch of money on Photoshop and instead use this in conjunction with free Gimp, etc.
Then gain, GIMP has a plug-in for content-aware fill already so you might want to test that out first. GIMP's plug-in (called resynthesizer) is more clunky to use than Photoshop's content-aware fill, but it's free like GIMP is and does work in OS X. resynthesizer was doing this before adobe too, but I don't know if resynthesizer gets better results or not since I haven't used it.
But, anyway... if you don't want to go through the hassle of installing GIMP and resynthesizer and you can't purchase Photoshop, there's this for 20 bucks. The results are certainly not horrible. The interface is clunky as it is ugly, but it DOES work.