I'm just learning about cubecart, and I read a brief description stating that cubcart can be used for downloadable products. I'm looking for a way to sell a downloadable video. Can cubecart be used for this?

Yes. Just choose "digital" instead of "tangible" as the product type when you are adding a product. Never done it myself but a lot of folks here have.

Most of the products in my store are downloadable. The process was VERY easy to set up.

Just upload the digital file anywhere in your hosting account (above public_html makes it impossible for anyone to steal it), and add the server link (something like /home/youraccount/products/productfile.zip) to the product.

CubeCart handles the download according to the settings you enter into the config.