The target market (ie, retailers and food service types) will understand the acronym perfectly. Point Of Sale systems have existed for a long time:

http://en.wikipedia.org/wiki/Point_of_sale

We had looked into other names and POS/point-of-sale was the most recognizable and familiar with storeowners. Yes, the acronym is a little unfortunate. :)

The acronym always makes me snicker but having dealt with some clients talk about their POS systems, it's a very widely used acronym. In fact, it was a big US company for which I was first part of a conference call where the acronym was used. I snickered in a "they're calling it an iPad? Really?"-way. Then I got used to it. Just like iPad.

I kind of cringed when I saw the name too. But I can understand why Shopify chose it. Potential customers are going to google for "POS" along with a handful of other keywords.

Working in retail as a teenager, the cash desk/terminal/whatever else you may call it was always called the Point of Sale.

The joke got old really fast when you actually use a POS.

I totally disagree. Anyone working in the retail sector (the target customer) will understand immediately what POS means since POS is a well-known business acronym.