If you have a good business plan your domain name will reflect that.
Short answer is that the more descriptive your domain name is regarding your product the better return on your dollar.
Sure random domain names can work out well, ie : Yahoo/Google but most people don't have millions of dollars to brand those names.
On of the most important things is for the name to be reasonably memorable and pronounceable. I've learned that thing from my own mistakes. With the requirement to keep domain names short, you can't go much into the description part anyway. Product names can be more elaborate though.
Yes, I can see using keywords would make a lot more sense than other things, and in fact that could circumvent the problem of using either a product name or general name-because if your products are all related then a couple of keywords in a phrase could have you covered.