I'll be the first to admit that Shopify (NYSE: SHOP) isn't a cheap stock. It has shot up over 260% since February of last year, and now trades for a nosebleed 17 times sales. At this point I would caution strongly against "backing up the truck."And yet, in its short time as a public company, Shopify has become one of my larger holdings, constituting 3% of my portfolio.