another use for the single ’ is the so-called ‘ironic quotation’—to put emphasis on a certain word or phrase (for instance to point out its inaccuracy) within an expression/idea that’s not your own, or just for a non-exact ‘quote’ or thought (like a cartoon bubble)—- not to be overused (!), but sometimes useful.
for example:
these ‘healthy’ meals sell for $1.99
apparently this ‘isn’t what she signed up for’
the new ‘security’ measures…. (if you’re pointing out that the aim is not security)
also, check out http://en.wikipedia.org/wiki/Quotation_mark
and, as you see above, single ’ can be used to surround an atypical word-use, or an unofficial title as well!