Before I list them, though, let me say that it’s an attractive, usable site. There are many horrible product sites out there, and you aren’t one of them. But, there’s room for improvement.

1. Get the screenshot “above the fold.” I have a decent monitor at 1280×1024 and I had to scroll down to see the UI. From context I’m guessing that FileMerge is included with the mac. If that’s the case, your *major selling point* is your UI. OK, so you probably have a few extra features, too–but beople are going to buy this on the strength of its UI. Get it front and center.

2. In short, too many words. You’ve got gobs of text that people don’t want to slog through. Distill it down. Which leads me to…

3. “Sell the sizzle, not the steak”. Benefits, not features. You have a laundry list of features; it reminds me of a product for Windows! Potential customers want to know how it can help them, not if it has feature X.*

* Ok, well, developers might be a slight exception. Still, though, you need to sell benefits while making features easily findable. A good example is the editor integration, which you definitely want to be easy to find (and to rank high on a search, too).

4. John Gruber’s quick review mentioned his favorite feature of hiding identical text. This is mentioned nowhere obvious on your site, and he thinks it’s your killer feature! Don’t know if a picture is better than a description here, but you should get the word out somehow..

Good luck, and happy sales.