While not everyone on your team has to be certified, this Computer World article recommends that at least one certified consultant on your project, if for no reason other than to provide 'cheap insurance' against expensive missteps with the CRM technology.
"In technology infrastructure products (such as network or OS), certification might well be dismissed as a "nice to know." But in applications that are evolving rapidly, certification is an ongoing process that must be renewed at least once a year (in the case of Salesforce.com's program, it's four times a year). This is because not only are things changing fairly quickly in the application features and use-cases, the object model and APIs are being extended on a regular basis. Somebody who wasn't keeping their certification up is more likely to do something the hard way (through custom code or an external Web service) even though there's a new internal capability that could get the job done for free."