Cost Benefit Analysis
First, I agree with AC#3 who pointed out that a Symantec marketing person might be a less than reliable source of information or insight on this issue.
Second, I think it's just as unreasonable to assume that encryption is too expensive as it is to assume that it's free. People should weigh both the costs *and* the benefits of using more vs. less secure storage, and measure those against realistic requirements. Most people and businesses should "default to secure" with respect not only to encryption but also to authentication, allowable locations and mandated retention/destruction of data, etc. because the cost/likelihood of compromise is just too high. If data has to traverse someone else's network or sit on someone else's storage, and performance goals etc. can be met with encryption, then encryption should probably be used even if the system would be "more efficient" without it.
Third, I'm hardly a disinterested party myself here. I'm the project leader for CloudFS (http://cloudfs.org/cloudfs-overview/) which addresses exactly these kinds of issues - not only at-rest and in-flight encryption which are both optional, but also other aspects of multi-tenant isolation and management for "unstructured" (file system) data. Of course, I'm not alone. The "senior partner" when it comes to storage security/privacy has to be Tahoe-LAFS (http://tahoe-lafs.org/trac/tahoe-lafs) which provides extremely strong guarantees in those areas at the cost of modest sacrifices in performance and functionality. Other entries in this area range from corporate-appliance players such as Nasuni and Cleversafe down to personal-software players such as SpiderOak and AeroFS. Enabling different tradeoffs between security, performance and usability is an active area of research and commercial competition, and we should all be wary of "this is the one answer" FUD.
Disclaimer: I'm an "associate" at Red Hat, but not speaking for Red Hat, yadda yadda.