Date a soulmate from Pinole, United States. I sometimes spend more time coming up with the Google Maps description than anything else I do for a client. Most business owners have heard of the elevator speech. If you met someone on an elevator who asked you what you do, and you knew they were a potential client, how would you describe your business in 10 floors in such a way that there would be a reason for a follow up.
This is how I view the shortest description offered among all local business search engines (LSE's.) 200 characters is about 40 words or less (spaces count.) If I am able to tell my client's story in 40 words or less, think how easy it will be to tell that story in 200 words.
Once again, Google has not told, and pundits don't seem to know, whether heavy keywording of the description is critical or not. I make the assumption that it is. (Now pundits are beginning to agree that keywording counts in this section) Knowing how Google commonly thinks, I want to make sure my description has keywords that reflect back to the categories. Keep in mind that Google's robots understand synonyms, so your description can use different words for the categories you have shown earlier.
Google would prefer that the description not merely repeat the categories and geographic information that is available in other places on the listing. In fact, at one point in 2010 they made it a rule that you couldn't have such information in the description. After howls of protest, the changed this rule back to allow such elements. I generally want to include information here that is going to create action on the part of the client AND I try to include keywords, too.
On an odd note, the location of the description on the listing is not particularly bold or more prominent than other elements. In fact the pictures will dominate if you have them. Note to Google. This description should be the central element on the listing when viewed.