read some of this , highlight site names and search google.
nutsandboltsmedia.com/does-your-website-really-need-ssl/
but basically if your website is doing some kind of credit card transaction , definitely
if your site forums are all private community an secure connection would help
if you have paid memberships an Secure connection would help
Do most of you purchase an SSL for your forums ?
im just going to show you some examples of forums that use a secure connection somewhere
heres a list or sites that bbpress.org likes.
bbpress.org/about/examples/
dalluva.com uses a secure connection on their register/login forms
support.advancedcustomfields.com/ doesnt use a secure connection even on their store on the rest of their site , they let users pay with paypal on the store
mojo-themes.com doesnt use a secure connection on sign up and forums but they use it for their store section
hub.jmonkeyengine.org/ doesnt use a secure connection
community.presscrew.com/ doesnt use a secure connection
swnk.org doesnt use a secure connection
tamrielfoundry.com/ doesnt use a secure connection
