Is there any difference for SEO purposes between adding content to the short description and long description when doing write-ups on individual items?

Answer

You want your Short Description to be 2 to 3 sentences and the rest of your content in the Long Description. Not only does the Short Description help you with SEO but it also used for marketplaces such as Google Products, TheFind, Amazon, etc. 

The Long Description is generally not sent to marketplaces and so it can, and often does, contain HTML such as bullet points.  While you can get fairly lengthy with the content in the Long Description field, most retailers prefer shorter bullet points to make it easier for the consumer to comprehend.

Importance of a Good Short Description

Oftentimes we see retailers entering just a few words for their Short Description but this is not recommended and can cause some unforeseen results with search engines and your marketing efforts. At a minimum all Short Descriptions should be at least 150 characters long.

Invest the time and energy on creating really good Short Descriptions that affectively describe the product.  Your efforts will be rewarded by consumers and search engines alike.