Because of a recent security issue with libyaml you may see the psych error:
You appear to have an outdated version of libyaml (0.1.4) installed on your system.
Prior to 0.1.6, libyaml is vulnerable to a heap overflow exploit from malicious YAML payloads.
Recently, a colleague posted an analysis about how much time is needed to build a bare-bones Spree Commerce site, which can be found here. As a result, many potential Spree users are very excited: for less than two days of development time, someone can go from nothing to making money. That’s great!