Stephanie Miller posted some subscriber view stats that were shared in a panel she was on at MarketingProf’s B2B Forum this month – some are surprising
and most are helpful when thinking about ways to engage with
subscribers:

• The increase in purchase value of email subscribers vs. non
  subscribers is 17%. That means, on average, the email subscriber bought
  17% more! (source: Forrester Research)
• B2B subscribers are twice as likely to consider email "spam"
  if it comes "too frequently." That means you need to think about the
  cadence of your messages. What we marketers think is not too frequent
  might be measured differently by our subscribers. (source:
  MarketingSherpa)
• It’s wonderful to see that most business professionals (87%)
  claim email has had some impact on their purchase decisions (source:
  Forrester Research )
• 85% of business professionals sign up for email programs. This
  is not how many sign up for YOUR offer, but how many sign up for ANY
  offer. Still, that means the opportunity pool is high and the value of
  email as an information tool still intact. (source: Return Path)
• The percentage of business people who regularly read business
  emails on their mobile devices (keyword "regularly") was 37%, up from
  30% just a year ago. (source: Exact Target)
• The percentage of professionals who bother to unsubscribe from
  email they no longer want was 22%. Consider your unsubscribes to be
  only one-quarter of the real picture!! (source: Return Path)
• For one program, only about 3% of email subscribers had read
  the privacy policy. Does that mean subscribers make assumptions about
  how you will treat their personal information? How do those assumptions
  square with your actual policies? It’s worth finding out. Start by
  asking your customer service folks if they’ve ever heard comments or
  feedback on this topic. (source: Citrix Online)

"No stat will give you the complete picture, but if you program is far
off these metrics, consider the true relevancy of the subscriber
experience you are creating." she says.

Source: Return Path