We've been using Ubiquiti's Unifi line for about two years now. We started out with just two UAP-PRO units. Our setup now consists of a USG, 2 UAP-AC-PROs, and a CloudKey.
We're a small church, running under 100 in weekly attendance, and operate a daycare center at the facility through the week. At our heaviest, we'll have a few dozen people connected to the network. Due to our location we're currently on a relatively slow (12/1) DSL connection.
Overall I really like their products and they come at a great price point. They're actively maintaining and updating their products; always adding or improving features. My only complaint would be the stability of their updates. Over the past several months they've had a few missteps, but I've found them to stand behind their products and are more than accomodating when it comes to addressing these issues.
Their support team is always available and willing to help, although sometimes it does take a while to find and address the actual issue. They've also reworked their testing and release process over the past few months to minimize these types of issues.
Despite the few issues I've run into, I'd still recommend giving them a try, especially if you're being cost-conscious.