should Apex domains (and records) be avoided?

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http://serverfault.com – I'm building an app that is hosted on Heroku. Heroku suggests that Apex Domains are a Very Bad Idea -- they suggest using CNAME records and a workaround service like Zerigo or DNSSimple. However, every other host I've used seems to have no issue with it. EngineYard is included in that list and they also host on Amazon EC2. Should I get away from using A records in favor of using CNAMEs with a Zerigo workaround in the future? Is this really only a concern for high-availability apps? Is Heroku just being paranoid? (HowTos)