I don't think the usability is great. I do a lot of work with customers on a shopping site in terms of usability and your site would bring up a few 'reds' on one of our tests. I hope these comments are useful.
The first page should click through onto the Product page if you click on one or other of the items. As it is, the colour changes so I'm waiting for something to happen but then I wonder if it's broken. (I spotted later that the name in the text is a link but I don't think that's obvious enough - at least make the image or the title clickable if you don't want to make the whole roll over a target)
Clicking on Product only makes the top navigation change - it's subtle but most customers won't spot it.
On the product page, what's the difference between Download and Purchase? What limits does Download put on the software? Does it work with features disabled or only for a limited time? Put a link through to the Versiontracker/Macupdate ratings - I'd like to be able to check them. And who are the reviews from? Tell me...even it's just 'User from NYC'
Some of the copy is good - some isn't. What do you mean by control in a basic manner? Something along the lines of choosing your own keyboard shortcut? It's not clear.
The point about Smart Browse is good. I'd move the 'Album Art' one up - it means more than Growl (or explain Growl for those who don't know what it is) - and don't mention the other apps at the start. Something like 'Using iTunes Music Store art means you know your album art will always good with higher resolution and better accuracy than other apps.' Incidentally, if using iTMS art is a selling point - is it allowed to be? Or do you need permission?
Make the screenshots bigger. I clicked to try to see them in more detail.
I thought one of them might show the skins you're talking about? I'd like more information about them - is it easy to make them? Will you offer more skins in the future? Will other people be able to submit them?
When you click Purchase - make the 4 person license have four people in the button - add the word buy rather than just have the wording. And what happens next? I'm not sure whether a tick box/radio button and a 'Buy' button wouldn't be a better call to mention. Is it users or computers? It's not clear.
What are my purchase options? How can I pay you - make it clear upfront (on the product page) what payment options there are? It might make a difference in how many people carry on.
Lastly $12.95 seems a lot for an iTunes controller (is there a widget included?) considering Synergy (which I guess was a market leader at some point) is only 5. I'd consider making it less - even $9.95 - you might get more purchasers.
