I haven't sold any yet, but am going to try. Just setup my Gumroad page and uploaded a first product, mainly as a test:

https://gumroad.com/products/vi_quick It's a vi quick-start tutorial I wrote a while ago. (Yes, vi, not vim :) It was before vim was very common.) I first wrote it at the request of two sysadmin friends and colleagues of mine, who were transitioning from Windows to Unix, and they later told me they found it useful in getting up to speed with editing files using vi.

More small products (apps and ebooks, on programming topics) are in the pipeline and I hope to release some over the following weeks and months, one at a time.

I sold a WordPress plugin for writers via Gumroad, sold a handful. This is compared to selling hundred of other types of basic products like pdfs, ebooks etc via the same platform. I promoted the plugin on ProductHunt, Twitter and via friends - not really directly with the intended audience which was a mistake. It was a fun experiment but I think most people are unfamiliar with buying software in that way. For the customer it doesn't seem like it will be a product that is supported.

About 6 years ago, I wrote and sold a dumb little modification for WP-eCommerce that added additional details to admin emails. I think I charged $20 one time fee.

I promoted it in forums and Q&A websites that asked specifically for the feature.

I think I sold 10-ish total? I was young.

Yes, we sell MakeAppIcon Desktop on Gumroad.

Overall they provide a nice looking store and easy integration. But it's hard to do trackings over the store.